U.S. patent application number 16/269982 was filed with the patent office on 2019-06-06 for reception device and reception method.
The applicant listed for this patent is Panasonic Intellectual Property Corporation of America. Invention is credited to Tomohiro KIMURA, Mikihiro OUCHI.
Application Number | 20190173727 16/269982 |
Document ID | / |
Family ID | 61163408 |
Filed Date | 2019-06-06 |
![](/patent/app/20190173727/US20190173727A1-20190606-D00000.png)
![](/patent/app/20190173727/US20190173727A1-20190606-D00001.png)
![](/patent/app/20190173727/US20190173727A1-20190606-D00002.png)
![](/patent/app/20190173727/US20190173727A1-20190606-D00003.png)
![](/patent/app/20190173727/US20190173727A1-20190606-D00004.png)
![](/patent/app/20190173727/US20190173727A1-20190606-D00005.png)
![](/patent/app/20190173727/US20190173727A1-20190606-D00006.png)
![](/patent/app/20190173727/US20190173727A1-20190606-D00007.png)
![](/patent/app/20190173727/US20190173727A1-20190606-D00008.png)
![](/patent/app/20190173727/US20190173727A1-20190606-D00009.png)
![](/patent/app/20190173727/US20190173727A1-20190606-D00010.png)
View All Diagrams
United States Patent
Application |
20190173727 |
Kind Code |
A1 |
KIMURA; Tomohiro ; et
al. |
June 6, 2019 |
RECEPTION DEVICE AND RECEPTION METHOD
Abstract
A reception device includes: a receiver that receives a
multiplexed signal; a first demapper that demaps the multiplexed
signal, with a second modulated symbol stream being included in the
multiplexed signal as an undetermined signal component, to generate
a first bit likelihood stream; a second demapper that demaps the
multiplexed signal, with a first modulated symbol stream being
included in the multiplexed signal as an undetermined signal
component, to generate a second bit likelihood stream; a first
decoder that performs error control decoding on the first bit
likelihood stream; and a second decoder that performs error control
decoding on the second bit likelihood stream. The multiplexed
signal is a signal on which the first modulated symbol stream and
the second modulated symbol stream are superposed, the second
modulated symbol stream being subjected to conversion in accordance
with the first modulated symbol stream in only a first
direction.
Inventors: |
KIMURA; Tomohiro; (Osaka,
JP) ; OUCHI; Mikihiro; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Corporation of America |
Torrance |
CA |
US |
|
|
Family ID: |
61163408 |
Appl. No.: |
16/269982 |
Filed: |
February 7, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2017/027832 |
Aug 1, 2017 |
|
|
|
16269982 |
|
|
|
|
62374166 |
Aug 12, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 1/0048 20130101;
H04L 27/3483 20130101; H04L 27/38 20130101; H04L 1/0054 20130101;
H04L 1/0055 20130101; H04L 1/0071 20130101 |
International
Class: |
H04L 27/34 20060101
H04L027/34; H04L 27/38 20060101 H04L027/38; H04L 1/00 20060101
H04L001/00 |
Claims
1. A reception device that receives a multiplexed signal into which
a plurality of data series have been multiplexed by superposition
coding, and derives the plurality of data series from the
multiplexed signal, the plurality of data series including a first
data series in a first layer and a second data series in a second
layer, the reception device comprising: a receiver configured to
receive the multiplexed signal; a first demapper configured to
demap the multiplexed signal, with a second modulated symbol stream
of the second data series being included in the multiplexed signal
as an undetermined signal component, to generate a first bit
likelihood stream of the first data series; a second demapper
configured to demap the multiplexed signal, with a first modulated
symbol stream of the first data series being included in the
multiplexed signal as an undetermined signal component, to generate
a second bit likelihood stream of the second data series; a first
decoder configured to perform error control decoding on the first
bit likelihood stream to derive the first data series; and a second
decoder configured to perform error control decoding on the second
bit likelihood stream to derive the second data series, wherein the
multiplexed signal received by the receiver is a signal on which
the first modulated symbol stream and the second modulated symbol
stream are superposed at a predetermined amplitude ratio, the first
modulated symbol stream being generated by mapping a first bit
stream of the first data series, the second modulated symbol stream
being generated by mapping a second bit stream of the second data
series and being subjected to conversion in accordance with the
first modulated symbol stream in only a first direction among the
first direction and a second direction perpendicular to each other
in a complex plane in which the first modulated symbol stream and
the second modulated symbol stream are represented.
2. The reception device according to claim 1, wherein the
multiplexed signal received by the receiver is a signal on which a
first modulated symbol in the first modulated symbol stream and a
second modulated symbol in the second modulated symbol stream are
superposed, and in which a polarity of a component that the second
modulated symbol includes in the first direction is subjected to a
reversal when a component that the first modulated symbol includes
in the first direction satisfies a predetermined condition.
3. The reception device according to claim 2, wherein the second
demapper demaps the multiplexed signal to generate the second bit
likelihood stream, based on a superposition constellation that is a
combination of a first constellation used to map the first bit
stream and a second constellation used to map the second bit
stream, and that reflects the reversal of the polarity.
4. The reception device according to claim 1, wherein the
multiplexed signal received by the receiver is a signal on which
the first modulated symbol stream and the second modulated symbol
stream are superposed, the first modulated symbol stream being
generated by mapping the first bit stream using a first
constellation in which a plurality of signal points are dispersed
in only the first direction among the first direction and the
second direction, the second modulated symbol stream being
generated by mapping the second bit stream using a second
constellation in which a plurality of signal points are dispersed
in both the first direction and the second direction and being
subjected to the conversion.
5. The reception device according to claim 4, wherein the
multiplexed signal received by the receiver is a signal on which
the first modulated symbol stream and the second modulated symbol
stream are superposed, the second modulated symbol stream being
generated by mapping the second bit stream using the second
constellation and being subjected to the conversion, the second
constellation being a constellation in which noise tolerance in the
first direction is higher than noise tolerance in the second
direction.
6. The reception device according to claim 4, wherein the
multiplexed signal received by the receiver is a signal on which
the first modulated symbol stream and the second modulated symbol
stream are superposed, the second modulated symbol stream being
generated by mapping the second bit stream using the second
constellation and being subjected to the conversion, the second
constellation being a constellation in which a multilevel number in
the first direction is smaller than a multilevel number in the
second direction.
7. The reception device according to claim 4, wherein the
multiplexed signal received by the receiver is a signal on which
(i) a first modulated symbol in the first modulated symbol stream,
(ii) a first component that a second modulated symbol in the second
modulated symbol stream includes in the first direction, and (iii)
a second component that the second modulated symbol includes in the
second direction are superposed, and a proportion of the first
component superposed on the multiplexed signal is higher than a
proportion of the second component superposed on the multiplexed
signal.
8. The reception device according to claim 4, wherein the
multiplexed signal received by the receiver is a signal on which a
first modulated symbol in the first modulated symbol stream and a
second modulated symbol in the second modulated symbol stream are
superposed, and in which a polarity of a component that the second
modulated symbol includes in the first direction is reversed when
the first modulated symbol corresponds to one of two signal points
adjacent to each other in the first constellation, and the polarity
is maintained when the first modulated symbol corresponds to the
other of the two signal points.
9. The reception device according to claim 1, further comprising:
an encoder that performs error control coding on the first data
series derived by the first decoder to generate a first bit stream
of the first data series; a mapper that maps the first bit stream
to generate the first modulated symbol stream; a delayer that
delays the multiplexed signal received by the receiver for a
predetermined time length; and a subtractor that subtracts the
first modulated symbol stream from the multiplexed signal delayed
by the delayer, wherein the second demapper demaps the multiplexed
signal, with the first modulated symbol stream being included in
the multiplexed signal as an undetermined signal component, to
generate the second bit likelihood stream, when a signal-to-noise
ratio of the multiplexed signal satisfies a predetermined
requirement, and demaps the multiplexed signal from which the first
modulated symbol stream has been subtracted to generate the second
bit likelihood stream, when the signal-to-noise ratio of the
multiplexed signal fails to satisfy the predetermined
requirement.
10. A reception method of receiving a multiplexed signal into which
a plurality of data series have been multiplexed by superposition
coding, and deriving the plurality of data series from the
multiplexed signal, the plurality of data series including a first
data series in a first layer and a second data series in a second
layer, the reception method comprising: receiving the multiplexed
signal; demapping the multiplexed signal, with a second modulated
symbol stream of the second data series being included in the
multiplexed signal as an undetermined signal component, to generate
a first bit likelihood stream of the first data series; demapping
the multiplexed signal, with a first modulated symbol stream of the
first data series being included in the multiplexed signal as an
undetermined signal component, to generate a second bit likelihood
stream of the second data series; performing error control decoding
on the first bit likelihood stream to derive the first data series;
and performing error control decoding on the second bit likelihood
stream to derive the second data series, wherein in receiving the
multiplexed signal, the multiplexed signal received is a signal on
which the first modulated symbol stream and the second modulated
symbol stream are superposed at a predetermined amplitude ratio,
the first modulated symbol stream being generated by mapping a
first bit stream of the first data series, the second modulated
symbol stream being generated by mapping a second bit stream of the
second data series and being subjected to conversion in accordance
with the first modulated symbol stream in only a first direction
among the first direction and a second direction perpendicular to
each other in a complex plane in which the first modulated symbol
stream and the second modulated symbol stream are represented.
11. The reception method according to claim 10, wherein in
receiving the multiplexed signal, the multiplexed signal received
is a signal on which a first modulated symbol in the first
modulated symbol stream and a second modulated symbol in the second
modulated symbol stream are superposed, and in which a polarity of
a component that the second modulated symbol includes in the first
direction is subjected to a reversal when a component that the
first modulated symbol includes in the first direction satisfies a
predetermined condition.
12. The reception method according to claim 11, wherein in
generating the second bit likelihood stream, the multiplexed signal
is demapped to generate the second bit likelihood stream, based on
a superposition constellation that is a combination of a first
constellation used to map the first bit stream and a second
constellation used to map the second bit stream, and that reflects
the reversal of the polarity.
13. The reception method according to claim 10, wherein in
receiving the multiplexed signal, the multiplexed signal received
is a signal on which the first modulated symbol stream and the
second modulated symbol stream are superposed, the first modulated
symbol stream being generated by mapping the first bit stream using
a first constellation in which a plurality of signal points are
dispersed in only the first direction among the first direction and
the second direction, the second modulated symbol stream being
generated by mapping the second bit stream using a second
constellation in which a plurality of signal points are dispersed
in both the first direction and the second direction and being
subjected to the conversion.
14. The reception method according to claim 13, wherein in
receiving the multiplexed signal, the multiplexed signal received
is a signal on which the first modulated symbol stream and the
second modulated symbol stream are superposed, the second modulated
symbol stream being generated by mapping the second bit stream
using the second constellation and being subjected to the
conversion, the second constellation being a constellation in which
noise tolerance in the first direction is higher than noise
tolerance in the second direction.
15. The reception method according to claim 13, wherein in
receiving the multiplexed signal, the multiplexed signal received
is a signal on which the first modulated symbol stream and the
second modulated symbol stream are superposed, the second modulated
symbol stream being generated by mapping the second bit stream
using the second constellation and being subjected to the
conversion, the second constellation being a constellation in which
a multilevel number in the first direction is smaller than a
multilevel number in the second direction.
16. The reception method according to claim 13, wherein in
receiving the multiplexed signal, the multiplexed signal received
is a signal on which (i) a first modulated symbol in the first
modulated symbol stream, (ii) a first component that a second
modulated symbol in the second modulated symbol stream includes in
the first direction, and (iii) a second component that the second
modulated symbol includes in the second direction are superposed,
and a proportion of the first component superposed on the
multiplexed signal is higher than a proportion of the second
component superposed on the multiplexed signal.
17. The reception method according to claim 13, wherein in
receiving the multiplexed signal, the multiplexed signal received
is a signal on which a first modulated symbol in the first
modulated symbol stream and a second modulated symbol in the second
modulated symbol stream are superposed, and in which a polarity of
a component that the second modulated symbol includes in the first
direction is reversed when the first modulated symbol corresponds
to one of two signal points adjacent to each other in the first
constellation, and the polarity is maintained when the first
modulated symbol corresponds to the other of the two signal
points.
18. The reception method according to claim 10, further comprising:
performing error control coding on the first data series that has
been derived to generate a first bit stream of the first data
series; mapping the first bit stream to generate the first
modulated symbol stream; delaying the multiplexed signal that has
been received for a predetermined time length; and subtracting the
first modulated symbol stream from the multiplexed signal that has
been delayed, wherein in generating the second bit likelihood
stream, the multiplexed signal is demapped, with the first
modulated symbol stream being included in the multiplexed signal as
an undetermined signal component, to generate the second bit
likelihood stream, when a signal-to-noise ratio of the multiplexed
signal satisfies a predetermined requirement, and the multiplexed
signal from which the first modulated symbol stream has been
subtracted is demapped to generate the second bit likelihood
stream, when the signal-to-noise ratio of the multiplexed signal
fails to satisfy the predetermined requirement.
19. A reception device comprising: a receiver configured to receive
a multiplexed signal on which a first modulated symbol stream and a
second modulated symbol stream are superposed at an amplitude
ratio, the first modulated symbol stream being generated by mapping
a first bit stream of a first data series, the second modulated
symbol stream being generated by mapping a second bit stream of a
second data series, the first modulated symbol stream and the
second modulated symbol stream being representable on a complex
plane extending in a first direction and a second direction
perpendicular to the first direction; a first demapper configured
to demap the multiplexed signal to generate a first bit likelihood
stream without removing the second modulated symbol stream from the
multiplexed signal; a second demapper configured to demap the
multiplexed signal to generate a second bit likelihood stream
without removing the first modulated symbol stream from the
multiplexed signal; a first decoder configured to perform error
control decoding on the first bit likelihood stream to derive the
first bit stream; and a second decoder configured to perform error
control decoding on the second bit likelihood stream to derive the
second bit stream, wherein the receiver configured to receive the
multiplexed signal on which the second modulated symbol stream is
converted in accordance with the first modulated symbol stream only
in the first direction on the complex plane.
20. The reception device according to claim 19, wherein the
receiver is configured to receive the multiplexed signal provided
for multiple access, wherein the first data series is provided for
the reception device, and wherein the second data series is
provided for another reception device.
21. The reception device according to claim 19, wherein the first
direction is provided along one of a real axis and an imaginary
axis of the complex plane.
22. The reception device according to claim 19, wherein the
receiver receives the multiplexed signal in which a polarity of a
real part of a second modulated symbol included in the second
modulated symbol stream is reversed and in which a first modulated
symbol included in the first modulated symbol stream has a positive
real part.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. continuation application of PCT
International Patent Application Number PCT/JP2017/027832 filed on
Aug. 1, 2017, claiming the benefit of priority of U.S. Provisional
Patent Application No. 62/374,166 filed on Aug. 12, 2016, the
entire contents of which are hereby incorporated by reference.
BACKGROUND
1. Technical Field
[0002] The present disclosure relates to a reception device and a
reception method.
2. Description of the Related Art
[0003] A multiplexing scheme utilizing superposition coding is
known as a scheme to multiplex and send a plurality of data series
(Seokhyun YOON and Donghee KIM, Performance of Superposition Coded
Broadcast/Unicast Service Overlay System, IEICE Transactions on
Communications, vol. E91-B, No. 9). Other known multiplexing
schemes include time division multiplexing and frequency division
multiplexing (Thomas M. Cover, Broadcast Channels, IEEE
Transactions on Information Theory, vol. IT-18, No. 1).
[0004] Compared to time division multiplexing and frequency
division multiplexing, the multiplexing scheme utilizing
superposition coding is suited to multiplexing a plurality of data
series that are required to have different levels of noise
tolerance (receiver tolerance). The multiplexing scheme utilizing
superposition coding is also termed as layer division multiplexing.
The multiplexing scheme utilizing superposition coding applied to
multiple access is also known as non-orthogonal division multiple
access (NOMA).
[0005] In the multiplexing scheme utilizing superposition coding, a
transmission device superposes a plurality of modulated symbols,
which are obtained by modulating each of a plurality of data
series, using predetermined power allocation, and transmits the
superposed modulated symbols. A reception device sequentially
demodulates the modulated symbols that are multiplexed by
superposition coding, starting with modulated symbols in a layer
with high noise tolerance until the completion of demodulating
modulated symbols in a layer to which a desired data series
belongs.
[0006] More specifically, the reception device demodulates the
modulated symbols in a layer with the highest noise tolerance to
estimate a data series. When a desired data series is yet to be
estimated, the reception device generates a replica of each
modulated symbol from another data series that has been estimated
to cancel the replica from the received signal, and demodulates
modulated symbols in a layer with the second highest noise
tolerance to estimate another data series. The reception device
repeats these processes until the desired data series is
estimated.
SUMMARY
[0007] A reception device according to an aspect of the present
disclosure is a reception device that receives a multiplexed signal
into which a plurality of data series have been multiplexed by
superposition coding, and derives the plurality of data series from
the multiplexed signal, the plurality of data series including a
first data series in a first layer and a second data series in a
second layer, the reception device including: a receiver that
receives the multiplexed signal; a first demapper that demaps the
multiplexed signal, with a second modulated symbol stream of the
second data series being included in the multiplexed signal as an
undetermined signal component, to generate a first bit likelihood
stream of the first data series; a second demapper that demaps the
multiplexed signal, with a first modulated symbol stream of the
first data series being included in the multiplexed signal as an
undetermined signal component, to generate a second bit likelihood
stream of the second data series; a first decoder that performs
error control decoding on the first bit likelihood stream to derive
the first data series; and a second decoder that performs error
control decoding on the second bit likelihood stream to derive the
second data series. The multiplexed signal received by the receiver
is a signal on which the first modulated symbol stream and the
second modulated symbol stream are superposed at a predetermined
amplitude ratio, the first modulated symbol stream being generated
by mapping a first bit stream of the first data series, the second
modulated symbol stream being generated by mapping a second bit
stream of the second data series and being subjected to conversion
in accordance with the first modulated symbol stream in only a
first direction among the first direction and a second direction
perpendicular to each other in a complex plane in which the first
modulated symbol stream and the second modulated symbol stream are
represented.
[0008] Further merits and advantageous effects in one aspect of the
present disclosure will become apparent from the following
description and drawings. These merits and advantageous effects are
provided by the characteristics described in the following
description and drawings. However, not all of these merits and
advantageous effects are required to be provided, and thus one or
more of these merits and advantageous effects may be provided by
one or more of the characteristics described in the description and
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0009] These and other objects, advantages and features of the
disclosure will become apparent from the following description
thereof taken in conjunction with the accompanying drawings that
illustrate a specific embodiment of the present disclosure.
[0010] FIG. 1 is a block diagram of an example configuration of a
transmission device according to Embodiment 1;
[0011] FIG. 2 is a block diagram of an example configuration of a
reception device according to Embodiment 1;
[0012] FIG. 3 is a diagram showing transmission capacities in
superposition coding;
[0013] FIG. 4 is a diagram showing an example QPSK
constellation;
[0014] FIG. 5 is a diagram showing an example non-uniform
constellation;
[0015] FIG. 6 is a diagram showing transmission capacities in
superposition coding using QPSK and Nu-256QAM;
[0016] FIG. 7 is a block diagram of a first example configuration
of a reception device according to Embodiment 2;
[0017] FIG. 8 is a diagram showing an example superposition
constellation;
[0018] FIG. 9 is a flowchart of a first example of reception
operations according to Embodiment 2;
[0019] FIG. 10 is a diagram showing an example result of simulation
to compare sequential decoding and parallel decoding in
superposition coding;
[0020] FIG. 11 is a block diagram of a second example configuration
of the reception device according to Embodiment 2;
[0021] FIG. 12 is a flowchart of a second example of reception
operations according to Embodiment 2;
[0022] FIG. 13 is a block diagram of a first example configuration
of a transmission device according to Embodiment 3;
[0023] FIG. 14 is a block diagram of a second example configuration
of the transmission device according to Embodiment 3;
[0024] FIG. 15 is a block diagram of a third example configuration
of the transmission device according to Embodiment 3;
[0025] FIG. 16 is a block diagram of a first example configuration
of a reception device according to Embodiment 3;
[0026] FIG. 17 is a block diagram of a second example configuration
of the reception device according to Embodiment 3;
[0027] FIG. 18 is a block diagram of a third example configuration
of the reception device according to Embodiment 3;
[0028] FIG. 19 is a block diagram of a fourth example configuration
of the reception device according to Embodiment 3;
[0029] FIG. 20 is a diagram showing an example of a variation
superposition constellation according to Embodiment 3;
[0030] FIG. 21 is a flowchart of an example of transmission
operations according to Embodiment 3;
[0031] FIG. 22 is a flowchart of an example of reception operations
according to Embodiment 3;
[0032] FIG. 23 is a diagram showing an example result of simulation
to compare sequential decoding and parallel decoding in a variation
of superposition coding;
[0033] FIG. 24 is a block diagram showing a first example
configuration of a transmission device according to Embodiment
4;
[0034] FIG. 25 is a block diagram showing a second example
configuration of the transmission device according to Embodiment
4;
[0035] FIG. 26 is a block diagram showing a third example
configuration of the transmission device according to Embodiment
4;
[0036] FIG. 27 is a block diagram showing a first example
configuration of a reception device according to Embodiment 4;
[0037] FIG. 28 is a block diagram showing a second example
configuration of the reception device according to Embodiment
4;
[0038] FIG. 29 is a block diagram showing a third example
configuration of the reception device according to Embodiment
4;
[0039] FIG. 30 is a block diagram showing a fourth example
configuration of the reception device according to Embodiment
4;
[0040] FIG. 31 is a diagram showing an example of a BPSK
constellation;
[0041] FIG. 32 is a diagram showing a first example of a variation
superposition constellation according to Embodiment 4;
[0042] FIG. 33 is a flowchart of an example of transmission
operations according to Embodiment 4;
[0043] FIG. 34 is a flowchart of an example of reception operations
according to Embodiment 4;
[0044] FIG. 35 is a diagram showing an example of a constellation
based on PAM; and
[0045] FIG. 36 is a diagram showing a second example of the
variation superposition constellation according to Embodiment
4.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0046] In some cases, the multiplexing scheme utilizing
superposition coding fails to efficiently process a plurality of
data series.
[0047] For example, the multiplexing scheme utilizing superposition
coding is subjected to processing delays due to the process that
requires sequential decoding of a plurality of multiplexed data
series. Furthermore, the multiplexing scheme utilizing
superposition coding requires the reception device to include an
arithmetic resource, etc. for re-modulating a forward decoded data
series. The reception device is also required to include a memory
resource, etc. for holding received symbols used to decode the
subsequent data series, from when the previous data series is
decoded and re-modulated until when a modulated symbol stream of
the previous data series is obtained.
[0048] Moreover, the multiplexing scheme utilizing superposition
coding may suffer a decrease in transmission capacity due to a
plurality of superposed data series affecting each other.
[0049] The present disclosure provides exemplary embodiments that
solve the above-described problems involved in the multiplexing
scheme utilizing superposition coding. The present disclosure,
however, also provides an aspect that solves not completely but
partially the above-described problems, or an aspect that solves a
problem different from the above-described problems.
[0050] The following describes in detail the embodiments according
to the present disclosure with reference to the drawings. Note that
the following embodiments, etc. show a comprehensive or specific
illustration of the present disclosure. The numerical values,
shapes, materials, structural components, the arrangement and
connection of the structural components, steps, the processing
order of the steps, etc. shown in the following embodiments, etc.
are mere examples, and thus are not intended to limit the present
disclosure. Of the structural components described in the following
embodiments, etc. structural components not recited in any one of
the independent claims that indicate the broadest concepts of the
present disclosure will be described as optional structural
components.
[0051] Also note that encoding may mean error control coding. Error
control coding is also referred to as error-correcting coding.
Also, decoding may mean error control decoding. Error control
decoding is also referred to as error-correcting decoding or error
correction. Also, unknown may mean undetermined, and transmission
may mean sending.
Embodiment 1
[0052] The present embodiment describes multiplexing a plurality of
data series onto a plurality of layers by a multiplexing scheme
utilizing superposition coding, and transmitting the multiplexed
data series.
[0053] To simplify the description without loss of generality, the
present embodiment and other embodiments describe an example in
which two data series are multiplexed onto two different layers to
be transmitted. However, the multiplexing scheme described in the
present embodiment and other embodiments is applicable to three or
more data series multiplexed onto three or more different layers to
be transmitted.
[0054] Also, the present embodiment and other embodiments use a
first layer to which a first data series belongs as a layer with
higher noise tolerance than a second layer to which a second data
series belongs.
[0055] FIG. 1 shows an example configuration of transmission device
100 that multiplexes two data series onto two layers by
superposition coding, and transmits the multiplexed data series.
The configuration and operation of transmission device 100 will be
described with reference to FIG. 1.
[0056] Transmission device 100 includes encoder 111, interleaver
112, mapper 113, multiplier 114, encoder 121, interleaver 122,
mapper 123, multiplier 124, adder 130, and radio frequency unit (RF
unit) 140. These structural components may also be implemented as
dedicated or general-purpose circuits. Multiplier 114, multiplier
124, and adder 130 can also be represented collectively as a
superposer. RF unit 140 can also be represented as a transmitter.
RF unit 140 may include an antenna.
[0057] Encoder 111 encodes an inputted first data series on the
basis of a first error control coding scheme to generate a first
bit stream. Interleaver 112 permutes the bits in the first bit
stream generated by encoder 111 on the basis of a first permutation
rule. Such permutation is also referred to as interleaving.
[0058] Mapper 113 maps the first bit stream permuted by interleaver
112 in accordance with a first mapping scheme (a first modulation
scheme) to generate a first modulated symbol stream that includes a
plurality of first modulated symbols. In the mapping in accordance
with the first mapping scheme, mapper 113 maps each group of bits
that includes a first number of bits in the first bit stream onto
one of the signal points in a first constellation, in accordance
with the values of such a group of bits.
[0059] Encoder 121 encodes an inputted second data series on the
basis of a second error control coding scheme to generate a second
bit stream. Interleaver 122 permutes the bits in the second bit
stream generated by encoder 121 on the basis of a second
permutation rule. Such permutation is also referred to as
interleaving.
[0060] Mapper 123 maps the second bit stream permuted by
interleaver 122 in accordance with a second mapping scheme (a
second modulation scheme) to generate a second modulated symbol
stream that includes a plurality of second modulated symbols. In
the mapping in accordance with the second mapping scheme, mapper
123 maps each group of bits that includes a second number of bits
in the second bit stream onto one of the signal points in a second
constellation, in accordance with the values of such a group of
bits.
[0061] When a mapping scheme used is PSK modulation such as BPSK
and QPSK, or QAM modulation such as 16QAM and 64QAM, each modulated
symbol can be represented by a complex number, for example, with
the real part representing the magnitude of the in-phase component
and the imaginary part representing the magnitude of the orthogonal
component. Meanwhile, when a mapping scheme used is PAM modulation,
each modulated symbol can be represented by a real number.
[0062] Multiplier 114 multiplies each first modulated symbol in the
first modulated symbol stream by first amplitude coefficient
a.sub.1. Multiplier 124 multiplies each second modulated symbol in
the second modulated symbol stream by second amplitude coefficient
a.sub.2. Adder 130 superposes first modulated symbols multiplied by
first amplitude coefficient a.sub.1 and second modulated symbols
multiplied by second amplitude coefficient a.sub.2 to generate a
superposed modulated symbol stream that includes a plurality of
superposed modulated symbols.
[0063] RF unit 140 sends the generated superposed modulated symbol
stream as a signal. More specifically, RF unit 140 generates, from
the superposed modulated symbol stream generated by adder 130, a
radio-frequency signal as a signal corresponding to the superposed
modulated symbol stream to send such a radio-frequency signal from
the antenna.
[0064] Stated differently, the superposer constituted by multiplier
114, multiplier 124, and adder 130 superposes the first modulated
symbol stream and the second modulated symbol stream at a
predetermined amplitude ratio, thereby generating a multiplexed
signal into which the first data series and the second data series
are multiplexed. Subsequently, RF unit 140 sends the multiplexed
signal. Note that the multiplexed signal corresponds to the
superposed modulated symbol stream. Also note that the
predetermined amplitude ratio may be 1:1, and that the
multiplication may be omitted.
[0065] FIG. 2 shows an example configuration of reception device
200 capable of receiving and sequentially decoding the signal on
which two data series are multiplexed onto two layers by
superposition coding, and capable of obtaining (extracting) one of
or both of the multiplexed two data series. The configuration and
operation of reception device 200 will be described with reference
to FIG. 2.
[0066] Reception device 200 includes RF unit 230, demapper 211,
deinterleaver 212, decoder 213, encoder 214, interleaver 215,
mapper 216, multiplier 217, delayer 218, subtractor 219, demapper
221, deinterleaver 222, and decoder 223. These structural
components may also be implemented as dedicated or general-purpose
circuits.
[0067] Demapper 211, deinterleaver 212, decoder 213, encoder 214,
interleaver 215, mapper 216, multiplier 217, delayer 218,
subtractor 219, demapper 221, deinterleaver 222, and decoder 223
can also be represented collectively as a deriver. RF unit 230 can
also be represented as a receiver. RF unit 230 may include an
antenna.
[0068] Reception device 200 receives by an antenna the multiplexed
signal sent from transmission device 100, and inputs such a
multiplexed signal into RF unit 230. Stated differently, RF unit
230 receives the multiplexed signal via the antenna. The
multiplexed signal received by RF unit 230 is also represented as a
received signal, and corresponds to the superimposed modulated
symbol stream into which the first modulated symbol stream and the
second modulated symbol stream are multiplexed. RF unit 230
generates a baseband received signal from the radio-frequency
received signal.
[0069] Demapper 211 demaps the baseband received signal on the
basis of the first constellation of the first mapping scheme to
generate a first bit likelihood stream. For example, amplitude
coefficient a.sub.1 is reflected in the first constellation for
demapping.
[0070] Deinterleaver 212 permutes the first bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
first permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 213 performs decoding that is based on the
first error control coding scheme by use of the first bit
likelihood stream permuted by deinterleaver 212, and outputs the
decoding result as the first data series.
[0071] Here, of the received signal corresponding to the superposed
modulated symbol stream, demapper 211 treats the components
corresponding to the second modulated symbols in the second data
series as an unknown signal (noise), and performs demapping on the
basis of the first constellation of the first mapping scheme.
[0072] When only the first data series is to be obtained, reception
device 200 terminates the process upon completing the estimation of
the first data series. Meanwhile, when the second data series is to
be obtained in addition to the first data series, or when only the
second data series is to be obtained, reception device 200 performs
the processes described below to obtain the second data series.
[0073] Encoder 214 encodes the first data series obtained by
decoder 213 on the basis of the first error control coding scheme
to generate the first bit stream. Interleaver 215 permutes the bits
in the first bit stream generated by encoder 214 on the basis of
the first permutation rule. Such permutation is also referred to as
interleaving.
[0074] Mapper 216 maps the first bit stream permuted by interleaver
215 in accordance with the first mapping scheme to generate the
first modulated symbol stream that includes a plurality of first
modulated symbols. Multiplier 217 multiplies the first modulated
symbol stream outputted by mapper 216 by first amplitude
coefficient a.sub.1.
[0075] Delayer 218 delays the received signal outputted from RF
unit 230 during the time from when RF unit 230 outputs the baseband
received signal to when multiplier 217 outputs the reproduced first
modulated symbol stream.
[0076] Subtractor 219 subtracts, from the received signal delayed
by delayer 218, the first modulated symbol stream multiplied by
first amplitude coefficient a.sub.1 by multiplier 217. Through
this, subtractor 219 removes the components corresponding to the
first modulated symbols from the received signal on which the
components corresponding to the first modulated symbols, the
components corresponding to the second modulated symbols, and noise
are superposed. Subsequently, subtractor 219 outputs a signal on
which the components corresponding to the second modulated symbols
and noise are superposed as a signal corresponding to the second
modulated symbol stream.
[0077] Demapper 221 demaps the signal outputted from subtractor 219
on the basis of the second constellation of the second mapping
scheme to generate a second bit likelihood stream. For example,
amplitude coefficient a.sub.2 is reflected in the second
constellation for demapping.
[0078] Deinterleaver 222 permutes the second bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
second permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 223 decodes the second bit likelihood
stream permuted by deinterleaver 222 on the basis of the second
error control coding scheme, and outputs the decoding result as the
second data series.
[0079] Through the above processes, reception device 200 obtains
one of or both of the first data series and the second data series
from the signal received by the antenna.
<Superposition Coding>
[0080] The following describes superposition coding.
[0081] Using signal power P.sub.s(W), noise power P.sub.n(W), and
transmission bandwidth B(Hz), transmission capacity C.sub.T (bit/s)
is given as the Shannon limit by Equation 1.
[ Math . 1 ] C T = B log 2 ( 1 + P s P n ) ( Equation 1 )
##EQU00001##
[0082] Transmission capacity C(bit/s/Hz) per Hz normalized by the
transmission bandwidth is given by Equation 2.
[ Math . 2 ] C = log 2 ( 1 + P s P n ) ( Equation 2 )
##EQU00002##
[0083] In the following, "transmission capacity per Hz" will be
simply referred to as "transmission capacity".
[0084] In superposition coding of the first data series and the
second data series, signal power P.sub.s1(W) of the first layer
corresponding to the first data series, signal power P.sub.s2(W) of
the second layer corresponding to the second data series, and the
entire signal power P.sub.s(W) satisfy:
P.sub.s=P.sub.s1+P.sub.s2.
[0085] When demodulating the first layer, reception device 200
regards the components of the modulated symbols in the second layer
as unknown components superposed on the modulated symbols in the
first layer, i.e., noise. As such, transmission capacity C.sub.1 of
the first layer is given by Equation 3.
[ Math . 3 ] C 1 = log 2 ( 1 + P s 1 P s 2 + P n ) ( Equation 3 )
##EQU00003##
[0086] When reception device 200 demodulates the second layer, the
components of the modulated symbols in the first layer have already
been removed from the received signal. As such, transmission
capacity C.sub.2 of the second layer is given by Equation 4.
[ Math . 4 ] C 2 = log 2 ( 1 + P s 2 P n ) ( Equation 4 )
##EQU00004##
[0087] As shown by Equation 5, the total of transmission capacity
C.sub.1 of the first layer and transmission capacity C.sub.2 of the
second layer agrees with the Shannon limit.
[ Math . 5 ] C 1 + C 2 = log 2 ( 1 + P s 1 P s 2 + P n ) + log 2 (
1 + P s 2 P n ) = log 2 ( 1 + P s + P n P s 2 + P n ) + log 2 ( P s
2 + P n P n ) = log 2 ( P s + P n P n ) = log 2 ( 1 + P s P n ) (
Equation 5 ) ##EQU00005##
[0088] In the present embodiment, signal power P.sub.s1 of the
first layer corresponding to the first data series is proportional
to the second power of first amplitude coefficient a.sub.1, and
signal power P.sub.s2 of the second layer corresponding to the
second data series is proportional to the second power of second
amplitude coefficient a.sub.2. The allocation of signal power to a
plurality of layers is determined by an amplitude coefficient that
is multiplied to the modulated symbols of each layer.
[0089] FIG. 3 shows an example simulation result of each
transmission capacity when the ratio between signal power P.sub.s1
of the first layer and signal power P.sub.s2 of the second layer is
P.sub.s1:P.sub.s2=2:1. In FIG. 3, the lateral axis represents as dB
(decibel) the ratio of signal power P.sub.s to noise power P.sub.n
(SNR), and the vertical axis represents transmission capacity. In
FIG. 3, the dot-and-dash line indicates transmission capacity
C.sub.1 of the first layer, the broken line indicates transmission
capacity C.sub.2 of the second layer, and the solid line indicates
the total transmission capacity of transmission capacity C.sub.1 of
the first layer and transmission capacity C.sub.2 of the second
layer.
[0090] Note that SNR, which means a ratio of signal power to noise
power, is also referred to as a signal-to-noise power ratio or a
signal-to-noise ratio.
<Non-Uniform Constellation>
[0091] Transmission device 100 according to the present embodiment
can employ any mapping scheme for each of the first mapping scheme
and the second mapping scheme. Reception device 200 demodulates the
first layer, with the second modulated symbols of the second layer
remaining unknown. As such, a mapping scheme such as QPSK, for
example, that mainly supports a low SNR is suitable as the first
mapping scheme.
[0092] FIG. 4 shows an example QPSK constellation. More
specifically, four QPSK signal points are plotted in the complex
plane, with the lateral axis representing the real part (the real
component) and the vertical axis representing the imaginary part
(the imaginary component). In QPSK, a group of bits (00, 01, 10, or
11) is associated with a modulated symbol indicating a complex
number on the basis of the constellation shown in FIG. 4.
[0093] Meanwhile, the second layer is demodulated with the
modulated symbols in the first layer having been removed. As such,
the second mapping scheme may be a mapping scheme that utilizes
multilevel constellation supporting a high SNR.
[0094] Non-uniform constellations as disclosed in J. Zoellner and
N. Loghin, Optimization of High-order Non-uniform QAM
Constellations, IEEE International Symposium on Broadband
Multimedia Systems and Broadcasting 2013 have received recent
attention as multilevel constellations. Unlike conventional uniform
constellations that include uniformly spaced signal points, such as
a QAM constellation, a non-uniform constellation includes
ununiformly spaced signal points. In some cases, a mapping scheme
using a non-uniform constellation improves the transmission
capacity compared to a mapping scheme using a uniform
constellation.
[0095] FIG. 5 shows an example non-uniform constellation including
256 signal points (Nu-256QAM). In FIG. 5, 256 non-uniform
constellation signal points are plotted in the complex plane, with
the lateral axis representing the real part and the vertical axis
representing the imaginary part.
[0096] The following describes an example of using QPSK shown in
FIG. 4 as the first mapping scheme and Nu-256QAM shown in FIG. 5 as
the second mapping scheme in the multiplexing scheme that utilizes
superposition coding.
[0097] FIG. 6 shows an example simulation result of each
transmission capacity when the ratio between signal power P.sub.s1
of the first layer and signal power P.sub.s2 of the second layer is
P.sub.s1:P.sub.s2=2:1. In FIG. 6, the lateral axis represents as dB
(decibel) the ratio of signal power P.sub.s to noise power P.sub.n
(SNR), and the vertical axis represents transmission capacity. In
FIG. 6, the dot-and-dash line indicates transmission capacity
C.sub.1 of the first layer, and the broken line indicates
transmission capacity C.sub.2 of the second layer. A combination of
QPSK and Nu-256QAM achieves a transmission capacity that is close
to the limit shown in FIG. 3.
[0098] As described above, transmission device 100 according to the
present embodiment is capable of highly efficient multiplexing and
transmission of a plurality of data series by a multiplexing scheme
utilizing superposition coding. Reception device 200 is capable of
receiving a plurality of data series that have been multiplexed in
a highly efficient manner by the multiplexing scheme utilizing
superposition coding. Transmission device 100 and reception device
200 are also capable of increasing the transmission capacity by use
of a non-uniform constellation.
[0099] Note that permutation (interleaving and deinterleaving)
reduces the effects that may be caused when successive errors
occur. Permutation (interleaving and deinterleaving) also controls
the correspondence among bits included in codewords in error
correcting coding, modulated symbols, and bits included in such
modulated symbols. However, such permutation (interleaving and
deinterleaving) may be omitted.
[0100] Stated differently, interleaver 112 and interleaver 122 are
optional structural components, and thus may not be included in
transmission device 100. Similarly, deinterleaver 212, interleaver
215, and deinterleaver 222 are optional structural components, and
thus may not be included in reception device 200.
[0101] Interleaving and deinterleaving, however, make a pair. As
such, when transmission device 100 includes interleaver 112 and
interleaver 122, reception device 200 basically includes
deinterleaver 212, interleaver 215, and deinterleaver 222.
Meanwhile, when transmission device 100 does not include
interleaver 112 and interleaver 122, reception device 200 does not
include deinterleaver 212, interleaver 215, and deinterleaver
222.
[0102] Also, amplitude coefficient a.sub.1 may be reflected in the
mapping performed by mapper 216 of reception device 200. In such a
case, reception device 200 may omit the multiplication, and thus
may not include multiplier 217.
[0103] Error control coding on the first data series and the second
data series may be performed by an external device that is
different from transmission device 100. In such a case,
transmission device 100 may omit the error control coding, and may
not include encoder 111 and encoder 121.
Embodiment 2
<Parallel Decoding of Signal Obtained by Superposition
Coding>
[0104] The present embodiment describes a reception method for
parallel decoding of a signal obtained by superposition coding. The
configuration of the transmission device is the same as the
configuration of transmission device 100 shown in FIG. 1, and thus
will not be described. In parallel decoding in superposition
coding, the reception device treats the components of the modulated
symbol stream in the first layer as an unknown signal (noise) to
decode the second layer, without removing the components of the
modulated symbol stream in the first layer included in the received
signal.
[0105] FIG. 7 shows an example configuration of reception device
300 capable of receiving and performing parallel decoding on the
signal on which two data series are multiplexed onto two layers by
superposition coding, and capable of obtaining one of or both of
the multiplexed two data series. The configuration and operation of
reception device 300 will be described with reference to FIG.
7.
[0106] Reception device 300 includes RF unit 330, demapper 310,
deinterleaver 312, decoder 313, deinterleaver 322, and decoder 323.
These structural components may also be implemented as dedicated or
general-purpose circuits. Demapper 310, deinterleaver 312, decoder
313, deinterleaver 322, and decoder 323 can also be represented
collectively as a deriver. RF unit 330 can also be represented as a
receiver. RF unit 330 may include an antenna.
[0107] Reception device 300 receives by an antenna the multiplexed
signal sent from transmission device 100, and inputs such a
multiplexed signal into RF unit 330. Stated differently, RF unit
330 receives the multiplexed signal via the antenna. The
multiplexed signal received by RF unit 330 is also represented as a
received signal. RF unit 330 generates a baseband received signal
from the radio-frequency received signal.
[0108] Demapper 310 demaps the baseband received signal to generate
the first bit likelihood stream and the second bit likelihood
stream. For example, demapper 310 performs such demapping on the
basis of a superposition constellation that shows the arrangement
of the signal points of superposed modulated symbols obtained by
superposing the first modulated symbols and the second modulated
symbols by superposition coding.
[0109] The superposition constellation is determined in accordance
with the first constellation of the first mapping scheme, the
second constellation of the second mapping scheme, first amplitude
coefficient a.sub.1, first amplitude coefficient a.sub.2, etc.
[0110] FIG. 8 shows an example superposition constellation, which
is more specifically a combination of the QPSK constellation shown
in FIG. 4 and the Nu-256QAM constellation shown in FIG. 5. Even
more specifically, the Nu-256QAM constellation (256 signal points)
is placed on each of the four regions in the complex plane in
accordance with the four signal points of the QPSK constellation.
These four regions, each corresponding to Nu-256QAM constellation,
may partially overlap with each other.
[0111] Demapper 310 performs demapping on the basis of the
superposition constellation as shown in FIG. 8. Stated differently,
demapper 310 generates the first bit likelihood stream, with the
modulated symbol stream of the second layer remaining unknown, and
generates the second bit likelihood stream, with the modulated
symbol stream of the first layer remaining unknown.
[0112] Note that demapper 310 may use the first constellation of
the first mapping scheme to generate the first bit likelihood
stream, and may use the above-described superposition constellation
to generate the second bit likelihood stream.
[0113] The first constellation, when used to generate the first bit
likelihood stream, enables demapper 310 to reduce the number of
signal points that should be considered in generating the first bit
likelihood stream, compared to when the superposition constellation
is also used to generate the first bit likelihood stream. This thus
enables demapper 310 to reduce the number of arithmetic
computations.
[0114] Demapper 310 corresponds, for example, to the first demapper
that demaps the received signal to generate the first bit
likelihood stream and the second demapper that demaps the received
signal to generate the second bit likelihood stream. Demapper 310
may include the first demapper that demaps the received signal to
generate the first bit likelihood stream and the second demapper
that demaps the received signal to generate the second bit
likelihood stream.
[0115] Deinterleaver 312 permutes the first bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
first permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 313 decodes the first bit likelihood stream
permuted by deinterleaver 312 on the basis of the first error
control coding scheme, and outputs the decoding result as the first
data series.
[0116] Deinterleaver 322 permutes the second bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
second permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 323 decodes the second bit likelihood
stream permuted by deinterleaver 322 on the basis of the second
error control coding scheme, and outputs the decoding result as the
second data series.
[0117] Note that permutation (deinterleaving) may be omitted as in
the case of Embodiment 1. Stated differently, deinterleaver 312 and
deinterleaver 322 are optional structural components, and thus may
not be included in reception device 300.
[0118] Interleaving and deinterleaving, however, make a pair. As
such, when transmission device 100 includes interleaver 112 and
interleaver 122, reception device 300 basically includes
deinterleaver 312 and deinterleaver 322. Meanwhile, when
transmission device 100 does not include interleaver 112 and
interleaver 122, reception device 300 does not include
deinterleaver 312 and deinterleaver 322.
[0119] FIG. 9 is a flowchart of example operations performed by
reception device 300. First, RF unit 330 receives the multiplexed
signal into which the first data series and the second data series
are multiplexed (S101).
[0120] Next, demapper 310 demaps the multiplexed signal to generate
the first bit likelihood stream of the first data series (S102).
Demapper 310 demaps the multiplexed signal to generate the second
bit likelihood stream of the second data series (S103).
Deinterleaver 312 may deinterleave such a generated first bit
likelihood stream. Also, deinterleaver 322 may deinterleave such a
generated second bit likelihood stream.
[0121] Then, decoder 313 performs error control decoding on the
first bit likelihood stream to derive the first data series (S104).
Also, decoder 323 performs error control decoding on the second bit
likelihood stream to derive the second data series (S105).
[0122] Note that processes on the first bit likelihood stream
(generation, deinterleaving, and error control decoding) and
processes on the second bit likelihood stream (generation,
deinterleaving, and error control decoding) are basically performed
in parallel.
[0123] Reception device 300 as shown in FIG. 7 that performs
parallel decoding has lower performance in decoding the second
layer than that of reception device 200 as shown in FIG. 2 that
performs sequential decoding.
[0124] FIG. 10 shows an example simulation result of the
transmission capacity of the second layer when the ratio between
signal power P.sub.s1 of the first layer and signal power P.sub.s2
of the second layer is P.sub.s1:P.sub.s2=2:1. In FIG. 10, the
lateral axis represents as dB (decibel) the ratio of signal power
P.sub.s to noise power Pn (SNR), and the vertical axis represents
transmission capacity. In FIG. 10, the solid line indicates the
transmission capacity of the second layer when sequential decoding
is performed, and the broken line indicates the transmission
capacity of the second layer when parallel decoding is
performed.
[0125] As FIG. 10 shows, in the decoding of the second layer,
parallel decoding involves an increased SNR with respect to the
same transmission capacity and a decreased transmission capacity
with respect to the same SNR, compared to sequential decoding.
[0126] As described above, reception device 300 according to the
present embodiment that performs parallel decoding has lower
performance in decoding the second data series transmitted on the
second layer than that of reception device 200 that performs
sequential decoding. However, reception device 300 reduces the
number of structural components required for decoding the second
layer.
[0127] More specifically, reception device 300 eliminates the need
for encoder 214, interleaver 215, mapper 216, and multiplier 217
that are required by reception device 200 shown in FIG. 2
performing sequential decoding to reproduce the modulated symbol
stream of the first layer. Reception device 300 also eliminates the
need for delayer 218 that delays the received signal and subtractor
219 that removes the components of the modulated symbols in the
first layer reproduced from the received signal.
[0128] The circuit size can be thus reduced. Reception device 300
also requires a smaller number of arithmetic computations and lower
power consumption than those required by reception device 200.
[0129] Reception device 200 shown in FIG. 2 that performs
sequential decoding demodulates the first layer in the received
signal to obtain the first data series, generates the first
modulated symbol stream from the obtained first data series, and
then starts demodulating the second layer in the received signal to
obtain the second data series. Meanwhile, reception device 300
according to the present embodiment that performs parallel decoding
is capable of simultaneously obtaining the first data series and
the second data series in parallel, thereby reducing processing
delays.
[0130] Alternatively, the reception device may observe the SNR of
the received signal to make selection between parallel decoding to
be performed when the SNR is high and sequential decoding to be
performed when the SNR is low.
[0131] In such a case, reception device 200 shown in FIG. 2
includes, for example, a controller that makes selection between
sequential decoding and parallel decoding depending on the SNR.
Such a controller may be included in RF unit 230 or demapper 221.
Furthermore, demapper 221 is configured to perform demapping based
on the superposition constellation, which is described as an
operation performed by demapper 310 shown in FIG. 7, in addition to
demapping that is based on the second constellation.
[0132] Demapper 221 switches between demapping to be performed on
the signal outputted from subtractor 219 on the basis of the second
constellation and demapping to be performed on the signal outputted
from RF unit 230 on the basis of the superposition constellation.
For example, demapper 221 switches between these demapping
operations in accordance with a control signal from the
controller.
[0133] FIG. 11 shows an example configuration of reception device
400 that selectively performs parallel decoding and sequential
decoding. Reception device 400 includes RF unit 430, demapper 411,
deinterleaver 412, decoder 413, encoder 414, interleaver 415,
mapper 416, multiplier 417, delayer 418, subtractor 419, demapper
421, deinterleaver 422, and decoder 423. Structural components of
reception device 400 shown in FIG. 11 and structural components of
reception device 200 shown in FIG. 2 are basically the same.
[0134] However, demapper 421 of reception device 400 performs
demapping that is based on the superposition constellation in
addition to demapping that is based on the second constellation of
the second mapping scheme. For example, depending on the SNR,
demapper 421 switches between demapping to be performed on the
signal outputted from subtractor 419 on the basis of the second
constellation and demapping to be performed on the signal outputted
from RF unit 430 on the basis of the superposition
constellation.
[0135] Although the example shown in FIG. 11 omits a controller
that makes selection between sequential decoding and parallel
decoding depending on the SNR, the controller may be included in
demapper 421, in RF unit 430, or in reception device 400 as a new
structural component.
[0136] FIG. 12 is a flowchart of example operations performed by
reception device 400. First, RF unit 430 receives the multiplexed
signal into which the first data series and the second data series
are multiplexed (S201). Then, RF unit 430 determines whether the
multiplexed signal satisfies a predetermined requirement. The
predetermined requirement, for example, is that the SNR should be
higher than a predetermined threshold.
[0137] When the multiplexed signal satisfies the predetermined
requirement (Yes in S202), demapper 411 demaps the multiplexed
signal to generate the first bit likelihood stream of the first
data series (S203). Also, demapper 421 demaps the multiplexed
signal to generate the second bit likelihood stream of the second
data series (S204). Deinterleaver 412 may deinterleave such a
generated first bit likelihood stream. Also, deinterleaver 422 may
deinterleave such a generated second bit likelihood stream.
[0138] Decoder 413 performs error control decoding on the first bit
likelihood stream to derive the first data series (S205). Also,
decoder 423 performs error control decoding on the second bit
likelihood stream to derive the second data series (S206).
[0139] These operations (S203 to S206) are basically the same as
the operations (S102 to S105) shown in FIG. 9.
[0140] Meanwhile, when the multiplexed signal fails to satisfy the
predetermined requirement (No in S202), demapper 411 demaps the
multiplexed signal to generate the first bit likelihood stream of
the first data series (S207). Deinterleaver 412 may deinterleave
such a generated first bit likelihood stream. Then, decoder 413
performs error control decoding on the first bit likelihood stream
to derive the first data series (S208).
[0141] Next, encoder 414 performs error control coding on the first
data series to generate the first bit stream (S209). Interleaver
415 may interleave such a generated first bit stream. Then, mapper
416 maps the first bit stream to generate the first modulated
symbol stream (S210). Multiplier 417 may multiply the first
modulated symbol stream by amplitude coefficient a.sub.1.
[0142] Delayer 418 delays the multiplexed signal until the first
modulated symbol stream is generated (S211). Then, subtractor 419
subtracts the first modulated symbol stream from the multiplexed
signal (S212).
[0143] Next, demapper 421 demaps the multiplexed signal from which
the first modulated symbol stream has been subtracted to generate
the second bit likelihood stream (S213). Deinterleaver 422 may
deinterleave such a generated second bit likelihood stream. Then,
decoder 423 performs error control decoding on the second bit
likelihood stream to derive the second data series (S214).
[0144] Through these operations, reception device 400 performs
parallel decoding when the SNR is high, thereby reducing the number
of arithmetic computations and power consumption. Reception device
400 also performs parallel decoding when the SNR is high, thereby
reducing processing delays. Meanwhile, reception device 400
performs sequential decoding when the SNR is low, thereby
increasing the possibility of correctly decoding the second data
series.
[0145] Note that the first mapping scheme and the second mapping
scheme according to the present embodiment are basically the same
as the first mapping scheme and the second mapping scheme according
to Embodiment 1. Stated differently, the first constellation and
the second constellation according to the present embodiment are
basically the same as the first constellation and the second
constellation according to Embodiment 1. Any one of a uniform
constellation and a non-uniform constellation may be used as the
second mapping scheme.
Embodiment 3
<Variation of Superposition Coding (Modified Superposition
Coding)>
[0146] The present embodiment describes a method of multiplexing
and transmitting a plurality of data series by a variation of
superposition coding (modified superposition coding), which is a
modified version of the above-described superposition coding.
[0147] FIG. 13 shows an example configuration of transmission
device 500 that multiplexes two data series onto two layers by the
variation of superposition coding, and transmits a multiplexed data
series. The configuration and operation of transmission device 500
will be described with reference to FIG. 13.
[0148] Transmission device 500 includes encoder 511, interleaver
512, mapper 513, multiplier 514, encoder 521, interleaver 522,
mapper 523, converter 525, multiplier 524, adder 530, and RF unit
540. These structural components may also be implemented as
dedicated or general-purpose circuits. Multiplier 514, multiplier
524, and adder 530 can also be represented collectively as a
superposer. RF unit 540 can also be represented as a transmitter.
RF unit 540 may include an antenna.
[0149] Encoder 511 encodes an inputted first data series on the
basis of a first error control coding scheme to generate a first
bit stream. Interleaver 512 permutes the bits in the first bit
stream generated by encoder 511 on the basis of a first permutation
rule. Such permutation is also referred to as interleaving.
[0150] Mapper 513 maps the first bit stream permuted by interleaver
512 in accordance with a first mapping scheme to generate a first
modulated symbol stream that includes a plurality of first
modulated symbols. In the mapping in accordance with the first
mapping scheme, mapper 513 maps each group of bits that includes a
first number of bits in the first bit stream onto one of the signal
points in a first constellation in accordance with the values of
such a group of bits.
[0151] When PSK modulation such as BPSK and QPSK, or QAM modulation
such as 16QAM and 64QAM is used as the first mapping scheme, each
first modulated symbol can be represented by a complex number, for
example, with the real part representing the magnitude of the
in-phase component and the imaginary part representing the
magnitude of the orthogonal component. Meanwhile, when PAM
modulation is used as the first mapping scheme, each first
modulated symbol can be represented by a real number.
[0152] Encoder 521 encodes an inputted second data series on the
basis of a second error control coding scheme to generate a second
bit stream. Interleaver 522 permutes the bits in the second bit
stream generated by encoder 521 on the basis of a second
permutation rule. Such permutation is also referred to as
interleaving.
[0153] Mapper 523 maps the second bit stream permuted by
interleaver 522 in accordance with a second mapping scheme to
generate a second modulated symbol stream that includes a plurality
of second modulated symbols. In the mapping in accordance with the
second mapping scheme, mapper 523 maps each group of bits that
includes a second number of bits in the second bit stream onto one
of the signal points in a second constellation in accordance with
the values of such a group of bits.
[0154] When PSK modulation such as BPSK and QPSK, or QAM modulation
such as 16QAM and 64QAM is used as the second mapping scheme, each
second modulated symbol can be represented by a complex number, for
example, with the real part representing the magnitude of the
in-phase component and the imaginary part representing the
magnitude of the orthogonal component. Meanwhile, when PAM
modulation is used as the second mapping scheme, each second
modulated symbol can be represented by a real number. Any one of a
uniform constellation and a non-uniform constellation may be used
as the second mapping scheme.
[0155] Converter 525 converts each second modulated symbol to be
superposed with the corresponding first modulated symbol, on the
basis of the values of the bits used to generate such a first
modulated symbol. Through this, converter 525 converts the second
modulated symbol stream.
[0156] Multiplier 514 multiplies each first modulated symbol in the
first modulated symbol stream by first amplitude coefficient
a.sub.1. Multiplier 524 multiplies, by second amplitude coefficient
a.sub.2, each second modulated symbol in the second modulated
symbol stream converted by converter 525. Adder 530 superposes
first modulated symbols multiplied by first amplitude coefficient
a.sub.1 and second modulated symbols multiplied by second amplitude
coefficient a.sub.2 to generate a superposed modulated symbol
stream that includes a plurality of superposed modulated
symbols.
[0157] RF unit 540 sends the generated superposed modulated symbol
stream as a signal. More specifically, RF unit 540 generates, from
the superposed modulated symbol stream generated by adder 530, a
radio-frequency signal as a signal corresponding to the superposed
modulated symbol stream to send such a radio-frequency signal from
the antenna.
[0158] Stated differently, the superposer constituted by multiplier
514, multiplier 524, and adder 530 superposes the first modulated
symbol stream and the second modulated symbol stream at a
predetermined amplitude ratio, thereby generating a multiplexed
signal into which the first data series and the second data series
are multiplexed. Subsequently, RF unit 540 sends the multiplexed
signal. Note that the multiplexed signal corresponds to the
superposed modulated symbol stream. Also note that the
predetermined amplitude ratio may be 1:1, and that the
multiplication may be omitted.
[0159] The following shows an example case in which QPSK is used as
the first mapping scheme to describe the operation of converter
525.
[0160] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 513, and
b.sub.1(t) and b.sub.2(t) are a plurality of bits to be mapped onto
S.sub.1(t), modulated symbol S.sub.1(t) is given by Equation 6.
[ Math . 6 ] S 1 ( t ) = ( 2 b 1 ( t ) - 1 ) + i ( 2 b 2 ( t ) - 1
) 2 ( Equation 6 ) ##EQU00006##
[0161] Here, i denotes the imaginary unit. Modulated symbol
S.sub.1(t) may also be given by an equation in which one of or both
of the (positive/negative) polarities of the real part and the
imaginary part of Equation 6 are reversed. Bit b.sub.1(t) is a bit
that contributes to the real part of modulated symbol S.sub.1(t).
Bit b.sub.2(t) is a bit that contributes to the imaginary part of
modulated symbol S.sub.1(t).
[0162] Converter 525 converts, into S'.sub.2(t), the t-th modulated
symbol S.sub.2(t) in the second modulated symbol stream generated
by mapper 523, on the basis of b.sub.1(t) and b.sub.2(t) as shown
by Equation 7.
[Math. 7]
S'.sub.2(t)=(-1).sup.b.sup.1.sup.(t)Re[S.sub.2(t)]+i(-1).sup.b.sup.2.sup-
.(t)Im[S.sub.2(t)] (Equation 7)
[0163] Here, S'.sub.2(t) is the converted t-th modulated symbol in
the second modulated symbol stream. Re[S.sub.2(t)] is the value of
the real part of S.sub.2(t), and Im[S.sub.2(t)] is the value of the
imaginary part of S.sub.2(t). Modulated symbol S'.sub.2(t) may be
given by an equation in which one of or both of the polarities of
the real part and the imaginary part of Equation 7 are
reversed.
[0164] As described above, the variation of superposition coding
controls the polarities of the real part and the imaginary part of
each second modulated symbol in accordance with the values of the
bits to be mapped onto the first modulated symbol that is
superposed with such a second modulated symbol. Note that the
polarities of the real part and the imaginary part of each second
modulated symbol may be controlled in accordance with the first
modulated symbol that is superposed with such a second modulated
symbol. Also, the polarity of one of the real part and the
imaginary part of each second modulated symbol may be controlled,
or the polarities of both the real part and the imaginary part of
each second modulated symbol may be controlled.
[0165] FIG. 14 shows an example configuration of transmission
device 600 that multiplexes two data series onto two layers by the
variation of superposition coding, and transmits the multiplexed
data series. The configuration of transmission device 600 is
different from the configuration of transmission device 500. The
configuration and operation of transmission device 600 will be
described with reference to FIG. 14.
[0166] Transmission device 600 includes encoder 611, interleaver
612, mapper 613, multiplier 614, encoder 621, interleaver 622,
mapper 623, converter 625, multiplier 624, adder 630, and RF unit
640. These structural components may also be implemented as
dedicated or general-purpose circuits. Multiplier 614, multiplier
624, and adder 630 can also be represented collectively as a
superposer. RF unit 640 can also be represented as a transmitter.
RF unit 640 may include an antenna.
[0167] Encoder 611 encodes an inputted first data series on the
basis of a first error control coding scheme to generate a first
bit stream. Interleaver 612 permutes the bits in the first bit
stream generated by encoder 611 on the basis of a first permutation
rule. Such permutation is also referred to as interleaving.
[0168] Mapper 613 maps the first bit stream permuted by interleaver
612 in accordance with a first mapping scheme to generate a first
modulated symbol stream that includes a plurality of first
modulated symbols. In the mapping in accordance with the first
mapping scheme, mapper 613 maps each group of bits that includes a
first number of bits in the first bit stream onto one of the signal
points in a first constellation in accordance with the values of
such a group of bits.
[0169] Encoder 621 encodes an inputted second data series on the
basis of a second error control coding scheme to generate a second
bit stream. Interleaver 622 permutes the bits in the second bit
stream generated by encoder 621 on the basis of a second
permutation rule. Such permutation is also referred to as
interleaving.
[0170] Mapper 623 maps the second bit stream permuted by
interleaver 622 in accordance with a second mapping scheme to
generate a second modulated symbol stream that includes a plurality
of second modulated symbols. In the mapping in accordance with the
second mapping scheme, mapper 623 maps each group of bits that
includes a second number of bits in the second bit stream onto one
of the signal points in a second constellation in accordance with
the values of such a group of bits.
[0171] Converter 625 converts each second modulated symbol to be
superposed with the corresponding first modulated symbol, on the
basis of the generated first modulated symbol. Through this,
converter 625 converts the second modulated symbol stream.
[0172] Multiplier 614 multiplies each first modulated symbol in the
first modulated symbol stream by first amplitude coefficient
a.sub.1. Multiplier 624 multiplies, by second amplitude coefficient
a.sub.2, each second modulated symbol in the second modulated
symbol stream converted by converter 625. Adder 630 superposes
first modulated symbols multiplied by first amplitude coefficient
a.sub.1 and second modulated symbols multiplied by second amplitude
coefficient a.sub.2 to generate a superposed modulated symbol
stream that includes a plurality of superposed modulated
symbols.
[0173] RF unit 640 sends the generated superposed modulated symbol
stream as a signal. More specifically, RF unit 640 generates, from
the superposed modulated symbol stream generated by adder 630, a
radio-frequency signal as a signal corresponding to the superposed
modulated symbol stream to send such a radio-frequency signal from
the antenna.
[0174] Stated differently, the superposer constituted by multiplier
614, multiplier 624, and adder 630 superposes the first modulated
symbol stream and the second modulated symbol stream at a
predetermined amplitude ratio, thereby generating a multiplexed
signal into which the first data series and the second data series
are multiplexed. Subsequently, RF unit 640 sends the multiplexed
signal. Note that the multiplexed signal corresponds to the
superposed modulated symbol stream. Also note that the
predetermined amplitude ratio may be 1:1, and that the
multiplication may be omitted.
[0175] The following shows an example case in which QPSK is used as
the first mapping scheme to describe the operation of converter
625.
[0176] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 613, and
b.sub.1(t) and b.sub.2(t) are a plurality of bits to be mapped onto
S.sub.1(t), modulated symbol S.sub.1(t) is given by Equation 8.
[ Math . 8 ] S 1 ( t ) = ( 2 b 1 ( t ) - 1 ) + i ( 2 b 2 ( t ) - 1
) 2 ( Equation 8 ) ##EQU00007##
[0177] Here, i denotes the imaginary unit. Modulated symbol
S.sub.1(t) may also be given by an equation in which one of or both
of the polarities of the real part and the imaginary part of
Equation 8 are reversed. Bit b.sub.1(t) is a bit that contributes
to the real part of modulated symbol S.sub.1(t). Bit b.sub.2(t) is
a bit that contributes to the imaginary part of modulated symbol
S.sub.1(t).
[0178] Converter 625 converts, into S'.sub.2(t), the t-th modulated
symbol S.sub.2(t) in the second modulated symbol stream generated
by mapper 623, on the basis of modulated symbol S.sub.1(t) as shown
by Equation 9.
[Math. 9]
S'.sub.2(t)=-sgn(Re[S.sub.1(t)])Re[S.sub.2(t)]-isgn(Im[S.sub.1(t)])Im[S.-
sub.2(t)] (Equation 9)
[0179] Here, S'.sub.2(t) is the converted t-th modulated symbol in
the second modulated symbol stream. Re[S.sub.2(t)] is the value of
the real part of S.sub.2(t), and Im[S.sub.2(t)] is the value of the
imaginary part of S.sub.2(t). Also, sgn(Re[S.sub.1(t)]) is the
polarity of the real part of S.sub.1(t), and sgn(Im[S.sub.1(t)]) is
the polarity of the imaginary part of S.sub.1(t).
[0180] Modulated symbol S'.sub.2(t) may be given by an equation in
which one of or both of the polarities of the real part and the
imaginary part of Equation 9 are reversed. Note that the conversion
that is based on Equation 9 is substantially the same as the
conversion that is based on Equation 7.
[0181] As described above, the variation of superposition coding
controls the polarities of the real part and the imaginary part of
each second modulated symbol in accordance with the first modulated
symbol that is superposed with such a second modulated symbol. Note
that the polarities of the real part and the imaginary part of each
second modulated symbol may be controlled in accordance with the
values of the bits to be mapped onto the first modulated symbol
that is superposed with such a second modulated symbol. Also, the
polarity of one of the real part and the imaginary part of each
second modulated symbol may be controlled, or the polarities of
both the real part and the imaginary part of each second modulated
symbol may be controlled.
[0182] FIG. 15 shows an example configuration of transmission
device 700 that multiplexes two data series onto two layers by the
variation of superposition coding, and transmits the multiplexed
data series. The configuration of transmission device 700 is
different from the configurations of transmission devices 500 and
600. The configuration and operation of transmission device 700
will be described with reference to FIG. 15.
[0183] Transmission device 700 includes encoder 711, interleaver
712, mapper 713, multiplier 714, encoder 721, interleaver 722,
mapper 723, multiplier 724, adder 730, and RF unit 740. These
structural components may also be implemented as dedicated or
general-purpose circuits. Multiplier 714, multiplier 724, and adder
730 can also be represented collectively as a superposer. RF unit
740 can also be represented as a transmitter. RF unit 740 may
include an antenna. Mapper 723 may include a converter.
[0184] Encoder 711 encodes an inputted first data series on the
basis of a first error control coding scheme to generate a first
bit stream. Interleaver 712 permutes the bits in the first bit
stream generated by encoder 711 on the basis of a first permutation
rule. Such permutation is also referred to as interleaving.
[0185] Mapper 713 maps the first bit stream permuted by interleaver
712 in accordance with a first mapping scheme to generate a first
modulated symbol stream that includes a plurality of first
modulated symbols. In the mapping in accordance with the first
mapping scheme, mapper 713 maps each group of bits that includes a
first number of bits in the first bit stream onto one of the signal
points in a first constellation in accordance with the values of
such a group of bits.
[0186] Encoder 721 encodes an inputted second data series on the
basis of a second error control coding scheme to generate a second
bit stream. Interleaver 722 permutes the bits in the second bit
stream generated by encoder 721 on the basis of a second
permutation rule. Such permutation is also referred to as
interleaving.
[0187] Mapper 723 converts (modifies) a second mapping scheme in
accordance with the first bit stream to be mapped to the first
modulated symbol stream by mapper 713. Mapper 723 then maps the
second bit stream interleaved by interleaver 722 in accordance with
the second mapping scheme that has been converted in accordance
with the first bit stream. Through these processes, mapper 723
generates a second modulated symbol stream that includes a
plurality of second modulated symbols.
[0188] In the mapping in accordance with the second mapping scheme,
mapper 723 maps each group of bits that includes a second number of
bits in the second bit stream onto one of the signal points in a
second constellation in accordance with the values of such a group
of bits.
[0189] Multiplier 714 multiplies each first modulated symbol in the
first modulated symbol stream by first amplitude coefficient
a.sub.1. Multiplier 724 multiplies each second modulated symbol in
the second modulated symbol stream by second amplitude coefficient
a.sub.2. Adder 730 superposes first modulated symbols multiplied by
first amplitude coefficient a.sub.1 and second modulated symbols
multiplied by second amplitude coefficient a.sub.2 to generate a
superposed modulated symbol stream that includes a plurality of
superposed modulated symbols.
[0190] RF unit 740 sends the generated superposed modulated symbol
stream as a signal. More specifically, RF unit 740 generates, from
the superposed modulated symbol stream generated by adder 730, a
radio-frequency signal as a signal corresponding to the superposed
modulated symbol stream to send such a radio-frequency signal from
the antenna.
[0191] Stated differently, the superposer constituted by multiplier
714, multiplier 724, and adder 730 superposes the first modulated
symbol stream and the second modulated symbol stream at a
predetermined amplitude ratio, thereby generating a multiplexed
signal into which the first data series and the second data series
are multiplexed. Subsequently, RF unit 740 sends the multiplexed
signal. Note that the multiplexed signal corresponds to the
superposed modulated symbol stream. Also note that the
predetermined amplitude ratio may be 1:1, and that the
multiplication may be omitted.
[0192] The following shows an example case in which QPSK is used as
the first mapping scheme to describe the operation of mapper
723.
[0193] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 713, and
b.sub.1(t) and b.sub.2(t) are a plurality of bits to be mapped onto
S.sub.1(t), modulated symbol S.sub.1(t) is given by Equation
10.
[ Math . 10 ] S 1 ( t ) = ( 2 b 1 ( t ) - 1 ) + i ( 2 b 2 ( t ) - 1
) 2 ( Equation 10 ) ##EQU00008##
[0194] Here, i denotes the imaginary unit. Modulated symbol
S.sub.1(t) may also be given by an equation in which one of or both
of the polarities of the real part and the imaginary part of
Equation 10 are reversed. Bit b.sub.1(t) is a bit that contributes
to the real part of modulated symbol S.sub.1(t). Bit b.sub.2(t) is
a bit that contributes to the imaginary part of modulated symbol
S.sub.1(t).
[0195] Mapper 723 performs exclusive-OR between b.sub.1(t) and the
bit that most contributes to the real part of the second
constellation among the bits in the second bit stream inputted from
interleaver 722. Mapper 723 also performs exclusive-OR between
b.sub.2(t) and the bit that most contributes to the imaginary part
of the second constellation among the bits in the second bit stream
inputted from interleaver 722. Mapper 723 then maps the second bit
stream on which exclusive-OR has been performed, on the basis of
the second constellation.
[0196] Here, the bit that most contributes to the real part of the
second constellation is a bit that causes the polarity of the real
part of the second constellation to be reversed, for example, when
the value of such a bit is reversed from 0 to 1 or from 1 to 0.
Stated differently, the bit that most contributes to the real part
of the second constellation refers to a bit that causes the
negative/positive sign of the value of the real part of each
modulated symbol to be reversed, for example, when the value of
such a bit is reversed from 0 to 1 or from 1 to 0.
[0197] Similarly, the bit that most contributes to the imaginary
part of the second constellation is a bit that causes the polarity
of the imaginary part of the second constellation to be reversed,
for example, when the value of such a bit is reversed from 0 to 1
or from 1 to 0. Stated differently, the bit that most contributes
to the imaginary part of the second constellation refers to a bit
that causes the negative/positive sign of the value of the
imaginary part of each modulated symbol to be reversed when the
value of such a bit is reversed from 0 to 1 or from 1 to 0.
[0198] In the above description, mapper 723 converts the second bit
stream, thereby substantially converting the second mapping scheme
(the second constellation). However, mapper 723 may directly
convert the second mapping scheme (the second constellation)
without converting the second bit stream. Stated differently,
mapper 723 may convert the correspondence between groups of bits
and signal points in the second constellation.
[0199] Also, the conversion performed by mapper 723 may be
performed by the converter included in mapper 723.
[0200] As described above, the variation of superposition coding
controls the polarities of the real part and the imaginary part of
each second modulated symbol in accordance with the values of the
bits to be mapped onto the first modulated symbol that is
superposed with such a second modulated symbol. Note that the
polarities of the real part and the imaginary part of each second
modulated symbol may be controlled in accordance with the first
modulated symbol that is superposed with such a second modulated
symbol. Also, the polarity of one of the real part and the
imaginary part of each second modulated symbol may be controlled,
or the polarities of both the real part and the imaginary part of
each second modulated symbol may be controlled.
<Sequential Decoding of Signal Obtained by Variation of
Superposition Coding>
[0201] FIG. 16 shows an example configuration of reception device
800 capable of receiving and sequentially decoding the signal on
which two data series are multiplexed onto two layers by the
above-described variation of superposition coding, and capable of
obtaining one of or both of the multiplexed two data series. The
configuration and operation of reception device 800 will be
described with reference to FIG. 16.
[0202] Reception device 800 includes RF unit 830, demapper 811,
deinterleaver 812, decoder 813, encoder 814, interleaver 815,
mapper 816, multiplier 817, delayer 818, subtractor 819, converter
820, demapper 821, deinterleaver 822, and decoder 823. These
structural components may also be implemented as dedicated or
general-purpose circuits.
[0203] Demapper 811, deinterleaver 812, decoder 813, encoder 814,
interleaver 815, mapper 816, multiplier 817, delayer 818,
subtractor 819, converter 820, demapper 821, deinterleaver 822, and
decoder 823 can also be represented collectively as a deriver. RF
unit 830 can also be represented as a receiver. RF unit 830 may
include an antenna.
[0204] Reception device 800 receives by an antenna the multiplexed
signal sent from transmission device 500, 600, or 700, and inputs
such a multiplexed signal into RF unit 830. Stated differently, RF
unit 830 receives the multiplexed signal via the antenna. The
multiplexed signal received by RF unit 830 is also represented as a
received signal, and corresponds to the superposed modulated symbol
stream into which the first modulated symbol stream and the second
modulated symbol stream are multiplexed. RF unit 830 generates a
baseband received signal from the radio-frequency received
signal.
[0205] Demapper 811 demaps the baseband received signal on the
basis of the first constellation of the first mapping scheme to
generate the first bit likelihood stream. For example, amplitude
coefficient a.sub.1 is reflected in the first constellation for
demapping.
[0206] Deinterleaver 812 permutes the first bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
first permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 813 performs decoding that is based on the
first error control coding scheme by use of the first bit
likelihood stream permuted by deinterleaver 812, and outputs the
decoding result as the first data series.
[0207] Here, of the received signal corresponding to the superposed
modulated symbol stream, demapper 811 treats the components
corresponding to the second modulated symbols in the second data
series as an unknown signal (noise), and performs demapping on the
basis of the first constellation of the first mapping scheme.
[0208] When only the first data series is to be obtained, reception
device 800 terminates the process upon completing the estimation of
the first data series. Meanwhile, when the second data series is to
be obtained in addition to the first data series, or when only the
second data series is to be obtained, reception device 800 performs
the processes described below to obtain the second data series.
[0209] Encoder 814 encodes the first data series obtained by
decoder 813 on the basis of the first error control coding scheme
to generate the first bit stream. Interleaver 815 permutes the bits
in the first bit stream generated by encoder 814 on the basis of
the first permutation rule. Such permutation is also referred to as
interleaving.
[0210] Mapper 816 maps the first bit stream permuted by interleaver
815 in accordance with the first mapping scheme to generate the
first modulated symbol stream that includes a plurality of first
modulated symbols. Multiplier 817 multiplies the first modulated
symbol stream outputted by mapper 816 by first amplitude
coefficient a.sub.1.
[0211] Delayer 818 delays the received signal outputted from RF
unit 830 during the time from when RF unit 830 outputs the baseband
received signal to when multiplier 817 outputs the reproduced first
modulated symbol stream.
[0212] Subtractor 819 subtracts, from the received signal delayed
by delayer 818, the first modulated symbol stream multiplied by
first amplitude coefficient a.sub.1 by multiplier 817. Through
this, subtractor 819 removes the components corresponding to the
first modulated symbols from the received signal on which the
components corresponding to the first modulated symbols, the
components corresponding to the second modulated symbols, and noise
are superposed. Subsequently, subtractor 819 outputs a signal on
which the components corresponding to the second modulated symbols
and noise are superposed as a signal corresponding to the second
modulated symbol stream.
[0213] Converter 820 converts the signal outputted from subtractor
819 as a signal corresponding to the second modulated symbol stream
by use of the first bit stream reproduced through encoding,
interleaving, etc. Demapper 821 demaps the signal outputted by
converter 820 on the basis of the second constellation of the
second mapping scheme to generate the second bit likelihood stream.
For example, amplitude coefficient a.sub.2 is reflected in the
second constellation for demapping.
[0214] Deinterleaver 822 permutes the second bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
second permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 823 decodes the second bit likelihood
stream permuted by deinterleaver 822 on the basis of the second
error control coding scheme, and outputs the decoding result as the
second data series.
[0215] The following shows an example case in which QPSK is used as
the first mapping scheme to describe the operation of converter
820.
[0216] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 816, and
b.sub.1(t) and b.sub.2(t) are a plurality of bits to be mapped onto
S.sub.1(t), modulated symbol S.sub.1(t) is given by Equation
11.
[ Math . 11 ] S 1 ( t ) = ( 2 b 1 ( t ) - 1 ) + i ( 2 b 2 ( t ) - 1
) 2 ( Equation 11 ) ##EQU00009##
[0217] Here, i denotes the imaginary unit. Modulated symbol
S.sub.1(t) may also be given by an equation in which one of or both
of the polarities of the real part and the imaginary part of
Equation 11 are reversed. Bit b.sub.1(t) is a bit that contributes
to the real part of modulated symbol S.sub.1(t). Bit b.sub.2(t) is
a bit that contributes to the imaginary part of modulated symbol
S.sub.1(t).
[0218] Converter 820 converts, into S'.sub.2(t), signal S.sub.2(t)
corresponding to the t-th modulated symbol in the second modulated
symbol stream out of the signal outputted by subtractor 819, on the
basis of b.sub.1(t) and b.sub.2(t) as shown by Equation 12.
[Math. 12]
S'.sub.2(t)=(-1).sup.b.sup.1.sup.(t)Re[S.sub.2(t)]+i(-1).sup.b.sup.2.sup-
.(t)Im[S.sub.2(t)] (Equation 12)
[0219] Here, S'.sub.2(t) is the signal that has undergone the
conversion. Also, Re[S.sub.2(t)] is the value of the real part of
S.sub.2(t), and Im[S.sub.2(t)] is the value of the imaginary part
of S.sub.2(t). Signal S'.sub.2(t) that has undergone the conversion
may be given by an equation in which one of or both of the
polarities of the real part and the imaginary part of Equation 12
are reversed.
[0220] Through the above processes, reception device 800 obtains
one of or both of the first data series and the second data series
from the signal received by the antenna.
[0221] FIG. 17 shows an example configuration of reception device
900 capable of receiving and sequentially decoding the signal on
which two data series are multiplexed onto two layers by the
above-described variation of superposition coding, and capable of
obtaining one of or both of the multiplexed two data series. The
configuration of reception device 900 is different from the
configuration of reception device 800. The configuration and
operation of reception device 900 will be described with reference
to FIG. 17.
[0222] Reception device 900 includes RF unit 930, demapper 911,
deinterleaver 912, decoder 913, encoder 914, interleaver 915,
mapper 916, multiplier 917, delayer 918, subtractor 919, converter
920, demapper 921, deinterleaver 922, and decoder 923. These
structural components may also be implemented as dedicated or
general-purpose circuits.
[0223] Demapper 911, deinterleaver 912, decoder 913, encoder 914,
interleaver 915, mapper 916, multiplier 917, delayer 918,
subtractor 919, converter 920, demapper 921, deinterleaver 922, and
decoder 923 can also be represented collectively as a deriver. RF
unit 930 can also be represented as a receiver. RF unit 930 may
include an antenna.
[0224] Reception device 900 receives by an antenna the multiplexed
signal sent from transmission device 500, 600, or 700, and inputs
such a multiplexed signal into RF unit 930. Stated differently, RF
unit 930 receives the multiplexed signal via the antenna. The
multiplexed signal received by RF unit 930 is also represented as a
received signal, and corresponds to the superposed modulated symbol
stream into which the first modulated symbol stream and the second
modulated symbol stream are multiplexed. RF unit 930 generates a
baseband received signal from the radio-frequency received
signal.
[0225] Demapper 911 demaps the baseband received signal on the
basis of the first constellation of the first mapping scheme to
generate the first bit likelihood stream. For example, amplitude
coefficient a.sub.1 is reflected in the first constellation for
demapping.
[0226] Deinterleaver 912 permutes the first bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
first permutation rule. Such a permutation is also referred to as
deinterleaving. Decoder 913 performs decoding that is based on the
first error control coding scheme by use of the first bit
likelihood stream permuted by deinterleaver 912, and outputs the
decoding result as the first data series.
[0227] Here, of the received signal corresponding to the superposed
modulated symbol stream, demapper 911 treats the components
corresponding to the second modulated symbols in the second data
series as an unknown signal (noise), and performs demapping on the
basis of the first constellation of the first mapping scheme.
[0228] When only the first data series is to be obtained, reception
device 900 terminates the process upon completing the estimation of
the first data series. Meanwhile, when the second data series is to
be obtained in addition to the first data series, or when only the
second data series is to be obtained, reception device 900 performs
the processes described below to obtain the second data series.
[0229] Encoder 914 encodes the first data series obtained by
decoder 913 on the basis of the first error control coding scheme
to generate the first bit stream. Interleaver 915 permutes the bits
in the first bit stream generated by encoder 914 on the basis of
the first permutation rule. Such permutation is also referred to as
interleaving.
[0230] Mapper 916 maps the first bit stream permuted by interleaver
915 in accordance with the first mapping scheme to generate the
first modulated symbol stream that includes a plurality of first
modulated symbols. Multiplier 917 multiplies the first modulated
symbol stream outputted by mapper 916 by first amplitude
coefficient a.sub.1.
[0231] Delayer 918 delays the received signal outputted from RF
unit 930 during the time from when RF unit 930 outputs the baseband
received signal to when multiplier 917 outputs the reproduced first
modulated symbol stream.
[0232] Subtractor 919 subtracts, from the received signal delayed
by delayer 918, the first modulated symbol stream multiplied by
first amplitude coefficient a.sub.1 by multiplier 917. Through
this, subtractor 919 removes the components corresponding to the
first modulated symbols from the received signal on which the
components corresponding to the first modulated symbols, the
components corresponding to the second modulated symbols, and noise
are superposed. Subsequently, subtractor 919 outputs a signal on
which the components corresponding to the second modulated symbols
and noise are superposed as a signal corresponding to the second
modulated symbol stream.
[0233] Converter 920 converts the signal outputted from subtractor
919 as a signal corresponding to the second modulated symbol stream
by use of the first modulated symbol stream reproduced through
encoding, interleaving, mapping, etc. Demapper 921 demaps the
signal outputted by converter 920 on the basis of the second
constellation of the second mapping scheme to generate the second
bit likelihood stream. For example, amplitude coefficient a.sub.2
is reflected in the second constellation for demapping.
[0234] Deinterleaver 922 permutes the second bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
second permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 923 decodes the second bit likelihood
stream permuted by deinterleaver 922 on the basis of the second
error control coding scheme, and outputs the decoding result as the
second data series.
[0235] The following shows an example case in which QPSK is used as
the first mapping scheme to describe the operation of converter
920.
[0236] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 916, and
b.sub.1(t) and b.sub.2(t) are a plurality of bits to be mapped onto
S.sub.1(t), modulated symbol S.sub.1(t) is given by Equation
13.
[ Math . 13 ] S 1 ( t ) = ( 2 b 1 ( t ) - 1 ) + i ( 2 b 2 ( t ) - 1
) 2 ( Equation 13 ) ##EQU00010##
[0237] Here, i denotes the imaginary unit. Modulated symbol
S.sub.1(t) may also be given by an equation in which one of or both
of the polarities of the real part and the imaginary part of
Equation 13 are reversed. Bit b.sub.1(t) is a bit that contributes
to the real part of modulated symbol S.sub.1(t). Bit b.sub.2(t) is
a bit that contributes to the imaginary part of modulated symbol
S.sub.1(t).
[0238] Converter 920 converts, into S'.sub.2(t), signal S.sub.2(t)
corresponding to the t-th modulated symbol in the second modulated
symbol stream out of the signal outputted by subtractor 919, on the
basis of modulated symbol S.sub.1(t) as shown by Equation 14.
[Math. 14]
S'.sub.2(t)=-sgn(Re[S.sub.1(t)])Re[S.sub.2(t)]-isgn(Im[S.sub.1(t)])Im[S.-
sub.2(t)] (Equation 14)
[0239] Here, S'.sub.2(t) is the signal that has undergone the
conversion. Also, Re[S.sub.2(t)] is the value of the real part of
S.sub.2(t), and Im[S.sub.2(t)] is the value of the imaginary part
of S.sub.2(t). Also, sgn(Re[S.sub.1(t)]) is the polarity of the
real part of S.sub.1(t), and sgn(Im[S.sub.1(t)]) is the polarity of
the imaginary part of S.sub.1(t). Signal S'.sub.2(t) that has
undergone the conversion may be given by an equation in which one
of or both of the polarities of the real part and the imaginary
part of Equation 14 are reversed. Note that the conversion that is
based on Equation 14 is substantially the same as the conversion
that is based on Equation 12.
[0240] Through the above processes, reception device 900 obtains
one of or both of the first data series and the second data series
from the signal received by the antenna.
[0241] FIG. 18 shows an example configuration of reception device
1000 capable of receiving and sequentially decoding the signal on
which two data series are multiplexed onto two layers by the
above-described variation of superposition coding, and capable of
obtaining one of or both of the multiplexed two data series. The
configuration of reception device 1000 is different from the
configurations of reception devices 800 and 900. The configuration
and operation of reception device 1000 will be described with
reference to FIG. 18.
[0242] Reception device 1000 includes RF unit 1030, demapper 1011,
deinterleaver 1012, decoder 1013, encoder 1014, interleaver 1015,
mapper 1016, multiplier 1017, delayer 1018, subtractor 1019,
demapper 1021, deinterleaver 1022, and decoder 1023. These
structural components may also be implemented as dedicated or
general-purpose circuits.
[0243] Demapper 1011, deinterleaver 1012, decoder 1013, encoder
1014, interleaver 1015, mapper 1016, multiplier 1017, delayer 1018,
subtractor 1019, demapper 1021, deinterleaver 1022, and decoder
1023 can also be represented collectively as a deriver. RF unit
1030 can also be represented as a receiver. RF unit 1030 may
include an antenna. Demapper 1021 may include a converter.
[0244] Reception device 1000 receives by an antenna the multiplexed
signal sent from transmission device 500, 600, or 700, and inputs
such a multiplexed signal into RF unit 1030. Stated differently, RF
unit 1030 receives the multiplexed signal via the antenna. The
multiplexed signal received by RF unit 1030 is also represented as
a received signal, and corresponds to the superposed modulated
symbol stream into which the first modulated symbol stream and the
second modulated symbol stream are multiplexed. RF unit 1030
generates a baseband received signal from the radio-frequency
received signal.
[0245] Demapper 1011 demaps the baseband received signal on the
basis of the first constellation of the first mapping scheme to
generate the first bit likelihood stream. For example, amplitude
coefficient a.sub.1 is reflected in the first constellation for
demapping.
[0246] Deinterleaver 1012 permutes the first bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
first permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1013 performs decoding that is based on the
first error control coding scheme by use of the first bit
likelihood stream permuted by deinterleaver 1012, and outputs the
decoding result as the first data series.
[0247] Here, of the received signal corresponding to the superposed
modulated symbol stream, demapper 1011 treats the components
corresponding to the second modulated symbols in the second data
series as an unknown signal (noise), and performs demapping on the
basis of the first constellation of the first mapping scheme.
[0248] When only the first data series is to be obtained, reception
device 1000 terminates the process upon completing the estimation
of the first data series. Meanwhile, when the second data series is
to be obtained in addition to the first data series, or when only
the second data series is to be obtained, reception device 1000
performs the processes described below to obtain the second data
series.
[0249] Encoder 1014 encodes the first data series obtained by
decoder 1013 on the basis of the first error control coding scheme
to generate the first bit stream. Interleaver 1015 permutes the
bits in the first bit stream generated by encoder 1014 on the basis
of the first permutation rule. Such permutation is also referred to
as interleaving.
[0250] Mapper 1016 maps the first bit stream permuted by
interleaver 1015 in accordance with the first mapping scheme to
generate the first modulated symbol stream that includes a
plurality of first modulated symbols. Multiplier 1017 multiplies
the first modulated symbol stream outputted by mapper 1016 by first
amplitude coefficient a.sub.1.
[0251] Delayer 1018 delays the received signal outputted from RF
unit 1030 during the time from when RF unit 1030 outputs the
baseband received signal to when multiplier 1017 outputs the
reproduced first modulated symbol stream.
[0252] Subtractor 1019 subtracts, from the received signal delayed
by delayer 1018, the first modulated symbol stream multiplied by
first amplitude coefficient a.sub.1 by multiplier 1017. Through
this, subtractor 1019 removes the components corresponding to the
first modulated symbols from the received signal on which the
components corresponding to the first modulated symbols, the
components corresponding to the second modulated symbols, and noise
are superposed. Subsequently, subtractor 1019 outputs a signal on
which the components corresponding to the second modulated symbols
and noise are superposed as a signal corresponding to the second
modulated symbol stream.
[0253] Demapper 1021 demaps the signal outputted from subtractor
1019 as a signal corresponding to the second modulated symbol
stream on the basis of the second constellation of the second
mapping scheme to generate the second bit likelihood stream. Such a
process reflects the first bit stream reproduced through encoding,
interleaving, etc. For example, amplitude coefficient a.sub.2 is
reflected in the second constellation for demapping.
[0254] Deinterleaver 1022 permutes the second bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
second permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1023 decodes the second bit likelihood
stream permuted by deinterleaver 1022 on the basis of the second
error control coding scheme, and outputs the decoding result as the
second data series.
[0255] The following shows an example case in which QPSK is used as
the first mapping scheme to describe the operation of demapper
1021.
[0256] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 1016, and
b.sub.1(t) and b.sub.2(t) are a plurality of bits to be mapped onto
S.sub.1(t), modulated symbol S.sub.1(t) is given by Equation
15.
[ Math . 15 ] S 1 ( t ) = ( 2 b 1 ( t ) - 1 ) + i ( 2 b 2 ( t ) - 1
) 2 ( Equation 15 ) ##EQU00011##
[0257] Here, i denotes the imaginary unit. Modulated symbol
S.sub.1(t) may also be given by an equation in which one of or both
of the polarities of the real part and the imaginary part of
Equation 15 are reversed. Bit b.sub.1(t) is a bit that contributes
to the real part of modulated symbol SAX Bit b.sub.2(t) is a bit
that contributes to the imaginary part of modulated symbol SAX
Demapper 1021 demaps signal S.sub.2(t) outputted from subtractor
1019 as a signal corresponding to the t-th modulated symbol in the
second modulated symbol stream on the basis of the second
constellation of the second mapping scheme.
[0258] Demapper 1021 reverses the bit likelihood corresponding to
the bit that most contributes to the real part of the second
constellation in accordance with b.sub.1(t) among the bit
likelihoods in the bit likelihood stream obtained by demapping.
Demapper 1021 also reverses the bit likelihood corresponding to the
bit that most contributes to the imaginary part of the second
constellation in accordance with b.sub.2(t) among the bit
likelihoods in the bit likelihood stream obtained by demapping.
[0259] For example, demapper 1021 performs exclusive-OR between
b.sub.1(t) and the bit likelihood corresponding to the bit that
most contributes to the real part of the second constellation among
the bit likelihoods in the bit likelihood stream obtained by
demapping. Demapper 1021 also performs exclusive-OR between
b.sub.2(t) and the bit likelihood corresponding to the bit that
most contributes to the imaginary part of the second constellation
among the bit likelihoods in the bit likelihood stream obtained by
demapping.
[0260] Demapper 1021 then outputs the bit likelihood stream that
has undergone the above-described reversal processes as the second
bit likelihood stream.
[0261] In the above description, demapper 1021 converts the bit
likelihood stream, thereby substantially converting the second
mapping scheme (the second constellation). However, demapper 1021
may directly convert the second mapping scheme (the second
constellation) without converting the bit likelihood stream. Stated
differently, demapper 1021 may convert the correspondence between
groups of bits and signal points in the second constellation.
[0262] Also, the conversion performed by demapper 1021 may be
performed by the converter included in demapper 1021.
[0263] Through the above processes, reception device 1000 obtains
one of or both of the first data series and the second data series
from the signal received by the antenna.
<Parallel Decoding of Signal Obtained by Variation of
Superposition Coding>
[0264] The following describes a reception method for parallel
decoding of a signal obtained by the variation of superposition
coding according to the present embodiment. The configuration of
the transmission device is the same as the configuration of
transmission device 500 shown in FIG. 13, transmission device 600
shown in FIG. 14, or transmission device 700 shown in FIG. 15, and
thus will not be described. In parallel decoding in the variation
of superposition coding, the reception device treats the components
of the modulated symbol stream in the first layer as an unknown
signal (noise) to decode the second layer, without removing the
components of the modulated symbol stream in the first layer
included in the received signal.
[0265] FIG. 19 shows an example configuration of reception device
1100 capable of receiving and performing parallel decoding on the
signal on which two data series are multiplexed onto two layers by
the variation of superposition coding, and capable of obtaining one
of or both of the multiplexed two data series. The configuration
and operation of reception device 1100 will be described with
reference to FIG. 19.
[0266] Reception device 1100 includes RF unit 1130, demapper 1110,
deinterleaver 1112, decoder 1113, deinterleaver 1122, and decoder
1123. These structural components may also be implemented as
dedicated or general-purpose circuits. Demapper 1110, deinterleaver
1112, decoder 1113, deinterleaver 1122, and decoder 1123 can also
be represented collectively as a deriver. RF unit 1130 can also be
represented as a receiver. RF unit 1130 may include an antenna.
[0267] Reception device 1100 receives by an antenna the multiplexed
signal sent from transmission device 500, 600, or 700, and inputs
such a multiplexed signal into RF unit 1130. Stated differently, RF
unit 1130 receives the multiplexed signal via the antenna. The
multiplexed signal received by RF unit 1130 is also represented as
a received signal. RF unit 1130 generates a baseband received
signal from the radio-frequency received signal.
[0268] Demapper 1110 demaps the baseband received signal to
generate the first bit likelihood stream and the second bit
likelihood stream. For example, demapper 1110 performs demapping on
the basis of a variation superposition constellation that shows the
arrangement of signal points of superposed modulated symbols
obtained by superposing the first modulated symbols and the second
modulated symbols by the variation of superposition coding.
[0269] The variation superposition constellation is determined in
accordance with the first constellation of the first mapping
scheme, the second constellation of the second mapping scheme,
first amplitude coefficient a.sub.1, first amplitude coefficient
a.sub.2, etc.
[0270] FIG. 20 shows the variation superposition constellation that
supports the variation of superposition coding. More specifically,
the variation superposition constellation is a combination of the
QPSK constellation shown in FIG. 4 and the Nu-256QAM constellation
shown in FIG. 5.
[0271] Even more specifically, the Nu-256QAM constellation (256
signal points) is placed on each of the four regions in the complex
plane in accordance with the four signal points of the QPSK
constellation. These four regions, each corresponding to Nu-256QAM
constellation, may partially overlap with each other. The present
variation superposition constellation reflects the conversion
performed on the second modulated symbol stream.
[0272] For example, when the Nu-256QAM constellation is combined
with a signal point with a positive real part among the four signal
points of the QPSK constellation, the polarity of the real part of
the Nu-256QAM constellation is reversed. Also, for example, when
the Nu-256QAM constellation is combined with a signal point with a
positive imaginary part among the four signal points of the QPSK
constellation, the polarity of the imaginary part of the Nu-256QAM
constellation is reversed.
[0273] More specifically, a first signal point, a second signal
point, a third signal point, a fourth signal point, a fifth signal
point, and a sixth signal point are shown in FIG. 20. When the
polarity of the real part of the Nu-256QAM constellation is not
reversed, the first signal point and the third signal point
correspond to the same bit values of the second bit stream.
Similarly, when the polarity of the imaginary part of the Nu-256QAM
constellation is not reversed, the fourth signal point and the
sixth signal point correspond to the same bit values of the second
bit stream.
[0274] When the polarity of the real part of the Nu-256QAM
constellation is reversed, the first signal point and the second
signal point correspond to the same bit values of the second bit
stream. Also, when the polarity of the imaginary part of the
Nu-256QAM constellation is reversed, the fourth signal point and
the fifth signal point correspond to the same bit values of the
second bit stream. Stated differently, such reversal enables a
plurality of signal points that correspond to the same bit values
of the second bit stream to approach each other and converge. This
mitigates the effect of noise on demapping.
[0275] Demapper 1110 performs demapping on the basis of the
variation superposition constellation as shown in FIG. 20. Stated
differently, demapper 1110 generates the first bit likelihood
stream with the modulated symbol stream of the second layer
remaining unknown, and generates the second bit likelihood stream
with the modulated symbol stream of the first layer remaining
unknown.
[0276] Note that demapper 1110 may use the first constellation of
the first mapping scheme to generate the first bit likelihood
stream, and may use the above-described variation superposition
constellation to generate the second bit likelihood stream.
[0277] The first constellation, when used to generate the first bit
likelihood stream, enables demapper 1110 to reduce the number of
signal points that should be considered in generating the first bit
likelihood stream, compared to when the variation superposition
constellation is also used to generate the first bit likelihood
stream. This thus enables demapper 1110 to reduce the number of
arithmetic computations.
[0278] Demapper 1110 corresponds, for example, to the first
demapper that demaps the received signal to generate the first bit
likelihood stream and the second demapper that demaps the received
signal to generate the second bit likelihood stream. Demapper 1110
may include the first demapper that demaps the received signal to
generate the first bit likelihood stream and the second demapper
that demaps the received signal to generate the second bit
likelihood stream.
[0279] Demapper 1110 may convert the second bit likelihood stream
that is generated using not the variation superposition
constellation but the superposition constellation, in accordance
with the first bit likelihood stream. This enables demapper 1110 to
obtain the same second bit likelihood stream as the second bit
likelihood stream that is generated using the variation
superposition constellation.
[0280] Demapper 1110 may convert the multiplexed signal without
using the variation superposition constellation to obtain the same
second bit likelihood stream as the second bit likelihood stream
that is generated using the variation superposition
constellation.
[0281] Deinterleaver 1112 permutes the first bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
first permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1113 decodes the first bit likelihood
stream permuted by deinterleaver 1112 on the basis of the first
error control coding scheme, and outputs the decoding result as the
first data series.
[0282] Deinterleaver 1122 permutes the second bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
second permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1123 decodes the second bit likelihood
stream permuted by deinterleaver 1122 on the basis of the second
error control coding scheme, and outputs the decoding result as the
second data series.
[0283] Through the above processes, reception device 1100 obtains
one of or both of the first data series and the second data series
from the signal received by the antenna.
[0284] Note that transmission devices 500, 600, and 700, and
reception devices 800, 900, 1000, and 1100 may omit permutation
(interleaving and deinterleaving) as in the case of Embodiment 1.
Stated differently, their respective interleavers and
deinterleavers are optional structural components, and thus may not
be included in these devices.
[0285] Interleaving and deinterleaving, however, make a pair. As
such, when transmission devices 500, 600, and 700 include their
respective interleavers, reception devices 800, 900, 1000, and 1100
basically include their respective deinterleavers and interleavers.
Meanwhile, when transmission devices 500, 600, and 700 do not
include their respective interleavers, reception devices 800, 900,
1000, and 1100 do not include their respective deinterleavers and
interleavers.
[0286] Amplitude coefficient a.sub.1 may be reflected in the
mapping for generating the first modulated symbols performed in
reception devices 800, 900, and 1000. In such a case, the
multiplication of amplitude coefficient a.sub.1 may be omitted.
Reception devices 800, 900, and 1000 thus may not include
multipliers 817, 917, and 1017, respectively.
[0287] Error control coding on the first data series and the second
data series may be performed by an external device. In such a case,
transmission devices 500, 600, and 700 may omit error control
coding, and may not include encoders 511, 521, 611, 621, 711, and
721.
[0288] FIG. 21 is a flowchart of example operations performed by
transmission device 500. First, mapper 513 maps the first bit
stream of the first data series to generate the first modulated
symbol stream of the first data series (S301). Then, mapper 523
maps the second bit stream of the second data series to generate
the second modulated symbol stream of the second data series
(S302).
[0289] Converter 525 subjects the second modulated symbol stream to
conversion in accordance with the first modulation symbol stream
(S303). More specifically, converter 525 converts the second
modulated symbol stream in accordance with the first bit stream,
thereby subjecting the second modulated symbol stream to conversion
in accordance with the first modulated symbol stream.
[0290] Next, the superposer constituted by first multiplier 514,
second multiplier 524, and adder 530 superposes the first modulated
symbol stream and the second modulated symbol stream that has been
subjected to conversion in accordance with the first modulated
symbol stream at a predetermined amplitude ratio, thereby
generating the multiplexed signal (S304). RF unit 540 then sends
the generated multiplexed signal (S305).
[0291] Note that in the above operation example, transmission
device 500 converts the second modulated symbol stream in
accordance with the first bit stream, thereby subjecting the second
modulated symbol stream to conversion in accordance with the first
modulated symbol stream (S303). Alternatively, transmission device
500 may convert the second modulated symbol stream in accordance
with the first modulated symbol stream, as in the case of
transmission device 600, thereby subjecting the second modulated
symbol stream to conversion in accordance with the first modulated
symbol stream.
[0292] Alternatively, as in the case of transmission device 700,
transmission device 500 may convert the second bit stream or the
second mapping scheme (the second constellation) used to generate
the second modulated symbol stream, in accordance with the first
bit stream. Through this, the second modulated symbol stream may be
subjected to conversion in accordance with the first modulated
symbol stream. In such a case, the second bit stream or the second
mapping scheme is converted before the second modulated symbol
stream is generated.
[0293] Stated differently, the second bit stream, the second
mapping scheme, or the second modulated symbol stream may be
converted in accordance with the first bit stream or the first
modulated symbol stream, thereby subjecting the second modulated
symbol stream to conversion in accordance with the first modulated
symbol stream.
[0294] Converter 525 may subject the second modulated symbol stream
to conversion in accordance with the first modulated symbol stream,
thereby controlling the polarities of the real part and the
imaginary part of each modulated symbol in the second modulated
symbol stream. Through this, converter 525 may reverse the polarity
of the real part of each second modulated symbol when the real part
of the corresponding first modulated symbol satisfies a
predetermined real part condition, and may reverse the polarity of
the imaginary part of each second modulated symbol when the
imaginary part of the corresponding first modulated symbol
satisfies a predetermined condition.
[0295] The predetermined real part condition may be a condition
that the polarity of the real part should be a predetermined
polarity of the real part, or may be a condition that the real part
should be within a predetermined range of the real part greater
than or equal to one. The predetermined range of the real part
greater than or equal to one may be a positive range or a negative
range. Similarly, the predetermined imaginary part condition may be
a condition that the polarity of the imaginary part should be a
predetermined polarity of the imaginary part, or may be a condition
that the imaginary part should be within a predetermined range of
the imaginary part greater than or equal to one. The predetermined
range of the imaginary part greater than or equal to one may be a
positive range or a negative range.
[0296] FIG. 22 is a flowchart of example operations performed by
reception devices 800, 900, 1000, and 1100. First, the receiver
receives the multiplexed signal (S401). Here, the receiver is RF
unit 830 of reception device 800, RF unit 930 of reception device
900, RF unit 1030 of reception device 1000, or RF unit 1130 of
reception device 1100.
[0297] The multiplexed signal is a signal into which a plurality of
data series including the first data series in the first layer and
the second data series in the second layer are multiplexed. The
multiplexed signal is also a signal on which the first modulated
symbol stream and the second modulated symbol stream are superposed
at a predetermined amplitude ratio.
[0298] The first modulated symbol stream is a modulated symbol
stream that is generated by mapping the first bit stream of the
first data series. The second modulated symbol stream is a
modulated symbol stream that is generated by mapping the second bit
stream of the second data series, and that has been subjected to
conversion in accordance with the first modulated symbol
stream.
[0299] Next, the deriver derives at least one of the first data
series or the second data series from the multiplexed signal
(S402).
[0300] The deriver of reception device 800 is constituted, for
example, by demapper 811, deinterleaver 812, decoder 813, encoder
814, interleaver 815, mapper 816, multiplier 817, delayer 818,
subtractor 819, converter 820, demapper 821, deinterleaver 822, and
decoder 823.
[0301] The deriver of reception device 900 is constituted, for
example, by demapper 911, deinterleaver 912, decoder 913, encoder
914, interleaver 915, mapper 916, multiplier 917, delayer 918,
subtractor 919, converter 920, demapper 921, deinterleaver 922, and
decoder 923
[0302] The deriver of reception device 1000 is constituted, for
example, by demapper 1011, deinterleaver 1012, decoder 1013,
encoder 1014, interleaver 1015, mapper 1016, multiplier 1017,
delayer 1018, subtractor 1019, demapper 1021, deinterleaver 1022,
and decoder 1023
[0303] The deriver of reception device 1100 is constituted, for
example, by demapper 1110, deinterleaver 1112, decoder 1113,
deinterleaver 1122, and decoder 1123.
[0304] In accordance with the above operations, the multiplexed
signal is received into which the first modulated symbol stream and
the second modulated symbol stream that has been subjected to
conversion in accordance with the first modulated symbol stream are
multiplexed. Then, at least one of the first data series or the
second data series is derived from such a multiplexed signal.
Stated differently, such a configuration enables: the reception of
the multiplexed signal that has been superposed in such a manner
that reduces performance degradation at the time of parallel
decoding: and an efficient derivation of one of or both of the
first data series and the second data series from such a
multiplexed signal.
[0305] Reception device 1100 as shown in FIG. 19 that performs
parallel decoding has lower performance in decoding the second
layer than that of reception devices 800, 900, and 1000 as shown in
FIG. 16, FIG. 17, and FIG. 18 that perform sequential decoding.
[0306] FIG. 23 shows an example simulation result of the
transmission capacity of the second layer when the ratio between
signal power P.sub.s1 of the first layer and signal power P.sub.s2
of the second layer is P.sub.s1:P.sub.s2=2:1. In FIG. 23, the
lateral axis represents as dB (decibel) the ratio of signal power
P.sub.s to noise power P.sub.n (SNR), and the vertical axis
represents transmission capacity. In FIG. 23, the solid line
indicates the transmission capacity of the second layer when
sequential decoding is performed, and the broken line indicates the
transmission capacity of the second layer when parallel decoding is
performed.
[0307] As FIG. 23 shows, in the decoding of the second layer,
parallel decoding involves an increased SNR with respect to the
same transmission capacity and a decreased transmission capacity
with respect to the same SNR, compared to sequential decoding.
[0308] As described above, reception device 1100 according to the
present embodiment that performs parallel decoding has lower
performance in decoding the second data series transmitted on the
second layer than that of reception devices 800, 900, and 1000 that
perform sequential decoding. However, reception device 1100 reduces
the number of structural components required to decode the second
layer.
[0309] More specifically, reception device 1100 eliminates the need
for the structural components that are required by reception
devices 800, 900, and 1000 shown in FIG. 16, FIG. 17, and FIG. 18
performing sequential decoding to reproduce the modulated symbol
stream of the first layer. Stated differently, encoders 814, 914,
and 1014, interleavers 815, 915, and 1015, mappers 816, 916, and
1016, and multipliers 817, 917, and 1017 are not required.
[0310] Reception device 1100 also eliminates the need for delayers
818, 918, and 1018 that delay the received signal, and subtractors
819, 919, and 1019 that remove the components of the modulated
symbols in the first layer reproduced from the received signal.
[0311] The circuit size can be thus reduced. Reception device 1100
also requires a smaller number of arithmetic computations and lower
power consumption than those required by reception devices 800,
900, and 1000.
[0312] Reception devices 800, 900, and 1000 shown in FIG. 16, FIG.
17, and FIG. 18 that perform sequential decoding demodulate the
first layer in the received signal to obtain the first data series,
and generate the first modulated symbol stream from the obtained
first data series. Subsequently, reception devices 800, 900, and
1000 start demodulating the second layer in the received signal to
obtain the second data series.
[0313] Meanwhile, reception device 1100 according to the present
embodiment that performs parallel decoding is capable of
simultaneously obtaining the first data series and the second data
series in parallel, thereby reducing processing delays.
[0314] The reception device may observe the SNR of the received
signal to make selection between parallel decoding to be performed
when the SNR is high and sequential decoding to be performed when
the SNR is low.
[0315] In such a case, reception device 800 shown in FIG. 16
includes, for example, a controller that makes selection between
sequential decoding and parallel decoding depending on the SNR.
Such a controller may be included in RF unit 830 or demapper 821.
Furthermore, demapper 821 is configured to perform demapping based
on the variation superposition constellation, which is described as
an operation performed by demapper 1110 shown in FIG. 19, in
addition to demapping that is based on the second
constellation.
[0316] Demapper 821 switches between demapping to be performed on
the signal outputted from converter 820 on the basis of the second
constellation and demapping to be performed on the signal outputted
from RF unit 830 on the basis of the variation superposition
constellation. For example, demapper 821 switches between these
demapping operations in accordance with a control signal from the
controller.
[0317] Note that such a configuration is also obtained by a
combination of reception device 400 shown in FIG. 11, reception
device 800 (converter 820, demapper 821, etc.) shown in FIG. 16,
and reception device 1100 (demapper 1110, etc.) shown in FIG.
19.
[0318] Another configuration is that reception device 900 shown in
FIG. 17 includes, for example, a controller that makes selection
between sequential decoding and parallel decoding depending on the
SNR. Such a controller may be included in RF unit 930 or demapper
921. Furthermore, demapper 921 is configured to perform demapping
based on the variation superposition constellation, which is
described as an operation performed by demapper 1110 shown in FIG.
19, in addition to demapping that is based on the first bit stream
and the second constellation.
[0319] Demapper 921 switches between demapping to be performed on
the signal outputted from converter 920 on the basis of the second
constellation and demapping to be performed on the signal outputted
from RF unit 930 on the basis of the variation superposition
constellation. For example, demapper 921 switches between these
demapping operations in accordance with a control signal from the
controller.
[0320] Note that such a configuration is also obtained by a
combination of reception device 400 shown in FIG. 11, reception
device 900 (converter 920, demapper 921, etc.) shown in FIG. 17,
and reception device 1100 (demapper 1110, etc.) shown in FIG.
19.
[0321] Still another configuration is that reception device 1000
shown in FIG. 18 includes, for example, a controller that makes
selection between sequential decoding and parallel decoding
depending on the SNR. Such a controller may be included in RF unit
1030 or demapper 1021. Furthermore, demapper 1021 is configured to
perform demapping based on the variation superposition
constellation, which is described as an operation performed by
demapper 1110 shown in FIG. 19, in addition to demapping that is
based on the first bit stream and the second constellation.
[0322] Demapper 1021 switches between demapping to be performed on
the signal outputted from subtractor 1019 on the basis of the
second constellation and demapping to be performed on the signal
outputted from RF unit 1030 on the basis of the variation
superposition constellation. For example, demapper 1021 switches
between these demapping operations in accordance with a control
signal from the controller.
[0323] Note that such a configuration is also obtained by a
combination of reception device 400 shown in FIG. 11, reception
device 1000 (demapper 1021, etc.) shown in FIG. 18, and reception
device 1100 (demapper 1110, etc.) shown in FIG. 19.
[0324] As described above, reception devices 800, 900, and 1000
perform parallel decoding when the SNR is high, thereby reducing
the number of arithmetic computations and power consumption.
Reception devices 800, 900, and 1000 also perform parallel decoding
when the SNR is high, thereby reducing processing delays.
Meanwhile, reception devices 800, 900, and 1000 perform sequential
decoding when the SNR is low, thereby increasing the possibility of
correctly decoding the second data series.
[0325] Comparison between the transmission capacity in the
multiplexing scheme utilizing superposition coding shown in FIG. 10
and the transmission capacity in the multiplexing scheme utilizing
the variation of superposition coding shown in FIG. 23 presents the
findings described below.
[0326] The characteristics of the transmission capacities exhibited
by sequential decoding (indicated by the solid line) are the same
between the multiplexing scheme utilizing superposition coding
(FIG. 10) and the multiplexing scheme utilizing the variation of
superposition coding (FIG. 23). Meanwhile, the characteristics of
the transmission capacities exhibited by parallel decoding
(indicated by the broken line) are improved by use of the
multiplexing scheme utilizing the variation of superposition coding
(FIG. 23) compared to the multiplexing scheme utilizing the
superposition coding (FIG. 10). Stated differently, the
multiplexing scheme utilizing the variation of superposition coding
provides desirable results both in sequential decoding and parallel
decoding.
Embodiment 4
<Variation of Superposition Coding (Modified Superposition
Coding)>
[0327] The present embodiment describes a method of multiplexing a
plurality of data series using a variation of superposition coding
(modified superposition coding), which is a modified version of the
above-described superposition coding, and transmitting the
plurality of multiplexed data series.
[0328] FIG. 24 shows an example configuration of transmission
device 1200 that multiplexes two data series onto two layers using
the variation of superposition coding, and transmits a multiplexed
data series. The configuration and operation of transmission device
1200 is to be described with reference to FIG. 24.
[0329] Transmission device 1200 includes encoder 1211, interleaver
1212, mapper 1213, multiplier 1214, encoder 1221, interleaver 1222,
mapper 1223, converter 1225, multiplier 1224, adder 1230, and RF
unit 1240. These structural components may also be implemented as
dedicated or general-purpose circuits. Multiplier 1214, multiplier
1224, and adder 1230 can also be represented collectively as a
superposer. RF unit 1240 can also be represented as a transmitter.
RF unit 1240 may include an antenna.
[0330] Encoder 1211 encodes an inputted first data series on the
basis of a first error control coding scheme to generate a first
bit stream. Interleaver 1212 permutes the bits in the first bit
stream generated by encoder 1211 on the basis of a first
permutation rule. Such permutation is also referred to as
interleaving.
[0331] Mapper 1213 maps the first bit stream permuted by
interleaver 1212 in accordance with a first mapping scheme to
generate a first modulated symbol stream that includes a plurality
of first modulated symbols. In the mapping in accordance with the
first mapping scheme, mapper 1213 maps each group of bits that
includes a first number of bits in the first bit stream onto one of
the signal points in a first constellation in accordance with the
values of such a group of bits.
[0332] When PSK modulation such as BPSK and QPSK, or QAM modulation
such as 16QAM and 64QAM is used as the first mapping scheme, each
first modulated symbol can be represented by a complex number, for
example, with the real part representing the magnitude of the
in-phase component and the imaginary part representing the
magnitude of the orthogonal component. Meanwhile, when PAM
modulation is used as the first mapping scheme, each first
modulated symbol can be represented by a real number.
[0333] Encoder 1221 encodes an inputted second data series on the
basis of a second error control coding scheme to generate a second
bit stream. Interleaver 1222 permutes the bits in the second bit
stream generated by encoder 1221 on the basis of a second
permutation rule. Such permutation is also referred to as
interleaving.
[0334] Mapper 1223 maps the second bit stream permuted by
interleaver 1222 in accordance with a second mapping scheme to
generate a second modulated symbol stream that includes a plurality
of second modulated symbols. In the mapping in accordance with the
second mapping scheme, mapper 1223 maps each group of bits that
includes a second number of bits in the second bit stream onto one
of the signal points in a second constellation in accordance with
the values of such a group of bits.
[0335] When PSK modulation such as BPSK and QPSK, or QAM modulation
such as 16QAM and 64QAM is used as the second mapping scheme, each
second modulated symbol can be represented by a complex number, for
example, with the real part representing the magnitude of the
in-phase component and the imaginary part representing the
magnitude of the orthogonal component. Meanwhile, when PAM
modulation is used as the second mapping scheme, each second
modulated symbol can be represented by a real number. Any one of a
uniform constellation and a non-uniform constellation may be used
as the second mapping scheme.
[0336] Converter 1225 converts each second modulated symbol to be
superposed with the corresponding first modulated symbol, on the
basis of the values of the bits used to generate such a first
modulated symbol. Through this, converter 1225 converts the second
modulated symbol stream.
[0337] Multiplier 1214 multiplies each first modulated symbol in
the first modulated symbol stream by first amplitude coefficient
a.sub.1. Multiplier 1224 multiplies, by second amplitude
coefficient a.sub.2, each second modulated symbol in the second
modulated symbol stream converted by converter 1225.
[0338] Multiplier 1224 may multiply both the real part and the
imaginary part of each second modulated symbol by second amplitude
coefficient a.sub.2, or may multiply only one of the real part and
the imaginary part by second amplitude coefficient a.sub.2.
Alternatively, multiplier 1224 may multiply the real part and the
imaginary part of each second modulated symbol by different
amplitude coefficients.
[0339] For example, when a first modulated symbol is constituted by
only a real part, multiplier 1224 may multiply only the real part
of a second modulated symbol by second amplitude coefficient
a.sub.2. Multiplier 1224 does not need to multiply the imaginary
part of the second modulated symbol by an amplitude coefficient, or
may multiply the imaginary part by an amplitude coefficient smaller
than second amplitude coefficient a.sub.2.
[0340] Adder 1230 superposes first modulated symbols multiplied by
first amplitude coefficient a.sub.1 and second modulated symbols
multiplied by second amplitude coefficient a.sub.2 to generate a
superposed modulated symbol stream that includes a plurality of
superposed modulated symbols.
[0341] RF unit 1240 sends the generated superposed modulated symbol
stream as a signal. More specifically, RF unit 1240 generates, from
the superposed modulated symbol stream generated by adder 1230, a
radio-frequency signal as a signal corresponding to the superposed
modulated symbol stream to send such a radio-frequency signal from
the antenna.
[0342] Stated differently, the superposer constituted by multiplier
1214, multiplier 1224, and adder 1230 superposes the first
modulated symbol stream and the second modulated symbol stream at a
predetermined amplitude ratio, thereby generating a multiplexed
signal into which the first data series and the second data series
are multiplexed. Subsequently, RF unit 1240 sends the multiplexed
signal. Note that the multiplexed signal corresponds to the
superposed modulated symbol stream.
[0343] Also the predetermined amplitude ratio may be fixed (for
example, 1:1), and the multiplication may be omitted. In the
superposition of the first modulated symbol stream and the second
modulated symbol stream, an amplitude ratio constituted by a
proportion of the first modulated symbol stream, a proportion of
the real component of the second modulated symbol stream, and a
proportion of the imaginary component of the second modulated
symbol stream may be used as the predetermined amplitude ratio. The
proportion of one of the real component and the imaginary component
that is not included in the first modulated symbol stream may be
higher than the proportion of the other. Note that the proportion
can also be represented as weight.
[0344] The following shows an example case in which BPSK is used as
the first mapping scheme to describe the operation of converter
1225.
[0345] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 1213, and
b.sub.1(t) is a bit to be mapped onto S.sub.1(t), modulated symbol
S.sub.1(t) is given by Equation 16.
[Math. 16]
S.sub.1(t)=2b.sub.1(t)-1 (Equation 16)
[0346] Modulated symbol S.sub.1(t) may also be given by an equation
in which the (positive/negative) polarity in Equation 16 is
reversed. Converter 1225 converts, into S'.sub.2(t), the t-th
modulated symbol S.sub.2(t) in the second modulated symbol stream
generated by mapper 1223, on the basis of b.sub.1(t) as shown by
Equation 17.
[Math. 17]
S'.sub.2(t)=(-1).sup.b.sup.1.sup.(t)Re[S.sub.2(t)]+iIm[S.sub.2(t)]
(Equation 17)
[0347] Here, S'.sub.2(t) is the converted t-th modulated symbol in
the second modulated symbol stream. Further, i denotes the
imaginary unit. Re[S.sub.2(t)] is the value of the real part of
S.sub.2(t), and Im[S.sub.2(t)] is the value of the imaginary part
of S.sub.2(t). Modulated symbol S'.sub.2(t) may be given by an
equation in which one of or both of the polarities of the real part
and the imaginary part of Equation 17 are reversed.
[0348] As described above, the polarity of the real part of each
second modulated symbol is controlled in accordance with the values
of the bits to be mapped onto the first modulated symbol that is
superposed with such a second modulated symbol. Note that the
polarity of the real part of each second modulated symbol may be
controlled in accordance with the first modulated symbol that is
superposed with such a second modulated symbol.
[0349] In the above, superposition coding is performed on the real
part. Accordingly, a first modulated symbol is constituted by a
real component, and the real component of the first modulated
symbol and the real component of a second modulated symbol are
superposed on a single real component. However, superposition
coding may be performed on the imaginary part. Accordingly, a first
modulated symbol may be constituted by an imaginary component, and
the imaginary component of the first modulated symbol and the
imaginary component of a second modulated symbol may be superposed
on a single real component.
[0350] FIG. 25 shows an example configuration of transmission
device 1300 that multiplexes two data series onto two layers by the
variation of superposition coding, and transmits the multiplexed
data series. The configuration of transmission device 1300 is
different from the configuration of transmission device 1200. The
configuration and operation of transmission device 1300 will be
described with reference to FIG. 25.
[0351] Transmission device 1300 includes encoder 1311, interleaver
1312, mapper 1313, multiplier 1314, encoder 1321, interleaver 1322,
mapper 1323, converter 1325, multiplier 1324, adder 1330, and RF
unit 1340. These structural components may also be implemented as
dedicated or general-purpose circuits. Multiplier 1314, multiplier
1324, and adder 1330 can also be represented collectively as a
superposer. RF unit 1340 can also be represented as a transmitter.
RF unit 1340 may include an antenna.
[0352] Encoder 1311 encodes an inputted first data series on the
basis of a first error control coding scheme to generate a first
bit stream. Interleaver 1312 permutes the bits in the first bit
stream generated by encoder 1311 on the basis of a first
permutation rule. Such permutation is also referred to as
interleaving.
[0353] Mapper 1313 maps the first bit stream permuted by
interleaver 1312 in accordance with a first mapping scheme to
generate a first modulated symbol stream that includes a plurality
of first modulated symbols. In the mapping in accordance with the
first mapping scheme, mapper 1313 maps each group of bits that
includes a first number of bits in the first bit stream onto one of
the signal points in a first constellation in accordance with the
values of such a group of bits.
[0354] Encoder 1321 encodes an inputted second data series on the
basis of a second error control coding scheme to generate a second
bit stream. Interleaver 1322 permutes the bits in the second bit
stream generated by encoder 1321 on the basis of a second
permutation rule. Such permutation is also referred to as
interleaving.
[0355] Mapper 1323 maps the second bit stream permuted by
interleaver 1322 in accordance with a second mapping scheme to
generate a second modulated symbol stream that includes a plurality
of second modulated symbols. In the mapping in accordance with the
second mapping scheme, mapper 1323 maps each group of bits that
includes a second number of bits in the second bit stream onto one
of the signal points in a second constellation in accordance with
the values of such a group of bits.
[0356] Converter 1325 converts each second modulated symbol to be
superposed with the corresponding first modulated symbol, on the
basis of the generated first modulated symbol. Through this,
converter 1325 converts the second modulated symbol stream.
[0357] Multiplier 1314 multiplies each first modulated symbol in
the first modulated symbol stream by first amplitude coefficient
a.sub.1. Multiplier 1324 multiplies, by second amplitude
coefficient a.sub.2, each second modulated symbol in the second
modulated symbol stream converted by converter 1325.
[0358] Multiplier 1324 may multiply both the real part and the
imaginary part of a second modulated symbol by second amplitude
coefficient a.sub.2, or may multiply only one of the real part and
the imaginary part by second amplitude coefficient a.sub.2.
Alternatively multiplier 1324 may multiply the real part and the
imaginary part of a second modulated symbol by different amplitude
coefficients.
[0359] For example, when the first modulated symbol is constituted
by only a real part, multiplier 1324 may multiply only the real
part of a second modulated symbol by second amplitude coefficient
a.sub.2. Multiplier 1324 does not need to multiply the imaginary
part of the second modulated symbol by an amplitude coefficient, or
may multiply the imaginary part by an amplitude coefficient smaller
than second amplitude coefficient a.sub.2.
[0360] Adder 1330 superposes first modulated symbols multiplied by
first amplitude coefficient a.sub.1 and second modulated symbols
multiplied by second amplitude coefficient a.sub.2 to generate a
superposed modulated symbol stream that includes a plurality of
superposed modulated symbols.
[0361] RF unit 1340 sends the generated superposed modulated symbol
stream as a signal. More specifically, RF unit 1340 generates, from
the superposed modulated symbol stream generated by adder 1330, a
radio-frequency signal as a signal corresponding to the superposed
modulated symbol stream to send such a radio-frequency signal from
the antenna.
[0362] Stated differently, the superposer constituted by multiplier
1314, multiplier 1324, and adder 1330 superposes the first
modulated symbol stream and the second modulated symbol stream at a
predetermined amplitude ratio, thereby generating a multiplexed
signal into which the first data series and the second data series
are multiplexed. Subsequently, RF unit 1340 sends the multiplexed
signal. Note that the multiplexed signal corresponds to the
superposed modulated symbol stream.
[0363] Also the predetermined amplitude ratio may be fixed (for
example, 1:1), and the multiplication may be omitted. In the
superposition of the first modulated symbol stream and the second
modulated symbol stream, an amplitude ratio constituted by a
proportion of the first modulated symbol stream, a proportion of
the real component of the second modulated symbol stream, and a
proportion of the imaginary component of the second modulated
symbol stream may be used as the predetermined amplitude ratio. The
proportion of one of the real component and the imaginary component
that is not included in the first modulated symbol stream may be
higher than the proportion of the other. Note that the proportion
can also be represented as weight.
[0364] The following shows an example case in which BPSK is used as
the first mapping scheme to describe the operation of converter
1325.
[0365] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 1313, and
b.sub.1(t) is a bit to be mapped onto S.sub.1(t), modulated symbol
S.sub.1(t) is given by Equation 18.
[Math. 18]
S.sub.1(t)=2b.sub.1(t)-1 (Equation 18)
[0366] Modulated symbol S.sub.1(t) may also be given by an equation
in which the polarity in Equation 18 is reversed. Converter 1325
converts, into S'.sub.2(t), t-th modulated symbol S.sub.2(t) in the
second modulated symbol stream generated by mapper 1323, on the
basis of modulated symbol S.sub.1(t) as shown by Equation 19.
[Math. 19]
S'.sub.2(t)=-sgn(S.sub.1(t))Re[S.sub.2(t)]+iIm[S.sub.2(t)]
(Equation 19)
[0367] Here, i denotes the imaginary unit. S'.sub.2(t) is the
converted t-th modulated symbol in the second modulated symbol
stream. Re[S.sub.2(t)] is the value of the real part of S.sub.2(t),
and Im[S.sub.2(t)] is the value of the imaginary part of
S.sub.2(t). Also, sgn(S.sub.1(t)) is the polarity of
S.sub.1(t).
[0368] Modulated symbol S'.sub.2(t) may be given by an equation in
which one of or both of the polarities of the real part and the
imaginary part of Equation 19 are reversed. Note that the
conversion that is based on Equation 19 is substantially the same
as the conversion that is based on Equation 17.
[0369] As described above, the polarity of the real part of each
second modulated symbol is controlled in accordance with the first
modulated symbol that is superposed with such a second modulated
symbol. Note that the polarity of the real part of each second
modulated symbol may be controlled in accordance with the values of
the bits to be mapped onto the first modulated symbol that is
superposed with such a second modulated symbol.
[0370] In the above, superposition coding is performed on the real
part. Accordingly, a first modulated symbol is constituted by a
real component, and the real component of the first modulated
symbol and the real component of a second modulated symbol are
superposed on a single real component. However, superposition
coding may be performed on the imaginary part. Accordingly, a first
modulated symbol may be constituted by an imaginary component, and
the imaginary component of the first modulated symbol and the
imaginary component of a second modulated symbol may be superposed
on a single real component.
[0371] FIG. 26 shows an example configuration of transmission
device 1400 that multiplexes two data series onto two layers by the
variation of superposition coding, and transmits the multiplexed
data series. The configuration of transmission device 1400 is
different from the configurations of transmission devices 1200 and
1300. The configuration and operation of transmission device 1400
will be described with reference to FIG. 26.
[0372] Transmission device 1400 includes encoder 1411, interleaver
1412, mapper 1413, multiplier 1414, encoder 1421, interleaver 1422,
mapper 1423, multiplier 1424, adder 1430, and RF unit 1440. These
structural components may also be implemented as dedicated or
general-purpose circuits. Multiplier 1414, multiplier 1424, and
adder 1430 can also be represented collectively as a superposer. RF
unit 1440 can also be represented as a transmitter. RF unit 1440
may include an antenna. Mapper 1423 may include a converter.
[0373] Encoder 1411 encodes an inputted first data series on the
basis of a first error control coding scheme to generate a first
bit stream. Interleaver 1412 permutes the bits in the first bit
stream generated by encoder 1411 on the basis of a first
permutation rule. Such permutation is also referred to as
interleaving.
[0374] Mapper 1413 maps the first bit stream permuted by
interleaver 1412 in accordance with a first mapping scheme to
generate a first modulated symbol stream that includes a plurality
of first modulated symbols. In the mapping in accordance with the
first mapping scheme, mapper 1413 maps each group of bits that
includes a first number of bits in the first bit stream onto one of
the signal points in a first constellation in accordance with the
values of such a group of bits.
[0375] Encoder 1421 encodes an inputted second data series on the
basis of a second error control coding scheme to generate a second
bit stream. Interleaver 1422 permutes the bits in the second bit
stream generated by encoder 1421 on the basis of a second
permutation rule. Such permutation is also referred to as
interleaving.
[0376] Mapper 1423 converts (modifies) a second mapping scheme in
accordance with the first bit stream to be mapped to the first
modulated symbol stream by mapper 1413. Mapper 1423 then maps the
second bit stream interleaved by interleaver 1422 in accordance
with the second mapping scheme that has been converted in
accordance with the first bit stream. Through these processes,
mapper 1423 generates a second modulated symbol stream that
includes a plurality of second modulated symbols.
[0377] In the mapping in accordance with the second mapping scheme,
mapper 1423 maps each group of bits that includes a second number
of bits in the second bit stream onto one of the signal points in a
second constellation in accordance with the values of such a group
of bits.
[0378] Multiplier 1414 multiplies each first modulated symbol in
the first modulated symbol stream by first amplitude coefficient
a.sub.1. Multiplier 1424 multiplies each second modulated symbol in
the second modulated symbol stream by second amplitude coefficient
a.sub.2.
[0379] Multiplier 1424 may multiply both the real part and the
imaginary part of a second modulated symbol by second amplitude
coefficient a.sub.2, or may multiply only one of the real part and
the imaginary part by second amplitude coefficient a.sub.2.
Alternatively, multiplier 1424 may multiply the real part and the
imaginary part of a second modulated symbol by different amplitude
coefficients.
[0380] For example, when a first modulated symbol is constituted by
only a real part, multiplier 1424 may multiply only the real part
of a second modulated symbol by second amplitude coefficient
a.sub.2. Multiplier 1424 does not need to multiply the imaginary
part of the second modulated symbol by an amplitude coefficient, or
may multiply the imaginary part by an amplitude coefficient smaller
than second amplitude coefficient a.sub.2.
[0381] Adder 1430 superposes first modulated symbols multiplied by
first amplitude coefficient a.sub.1 and second modulated symbols
having the real parts multiplied by second amplitude coefficient
a.sub.2 to generate a superposed modulated symbol stream that
includes a plurality of superposed modulated symbols.
[0382] RF unit 1440 sends the generated superposed modulated symbol
stream as a signal. More specifically, RF unit 1440 generates, from
the superposed modulated symbol stream generated by adder 1430, a
radio-frequency signal as a signal corresponding to the superposed
modulated symbol stream to send such a radio-frequency signal from
the antenna.
[0383] Stated differently, the superposer constituted by multiplier
1414, multiplier 1424, and adder 1430 superposes the first
modulated symbol stream and the second modulated symbol stream at a
predetermined amplitude ratio, thereby generating a multiplexed
signal into which the first data series and the second data series
are multiplexed. Subsequently, RF unit 1440 sends the multiplexed
signal. Note that the multiplexed signal corresponds to the
superposed modulated symbol stream.
[0384] Also the predetermined amplitude ratio may be fixed (for
example, 1:1), and the multiplication may be omitted. In the
superposition of the first modulated symbol stream and the second
modulated symbol stream, an amplitude ratio constituted by a
proportion of the first modulated symbol stream, a proportion of
the real component of the second modulated symbol stream, and a
proportion of the imaginary component of the second modulated
symbol stream may be used as the predetermined amplitude ratio. The
proportion of one of the real component and the imaginary component
that is not included in the first modulated symbol stream may be
higher than the proportion of the other. Note that the proportion
can also be represented as weight.
[0385] The following shows an example case in which BPSK is used as
the first mapping scheme to describe the operation of mapper
1423.
[0386] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 1413, and
b.sub.1(t) is a bit to be mapped onto S.sub.1(t), modulated symbol
S.sub.1(t) is given by Equation 20.
[Math. 20]
S.sub.1(t)=2b.sub.1(t)-1 (Equation 20)
[0387] Modulated symbol stream S.sub.1(t) may also be given by an
equation in which the polarity in Equation 20 is reversed. Mapper
1423 performs exclusive-OR between b.sub.1(t) and the bit that most
contributes to the real part of the second constellation among the
bits in the second bit stream inputted from interleaver 1422.
Mapper 1423 then maps the second bit stream on which exclusive-OR
has been performed, on the basis of the second constellation.
[0388] Here, the bit that most contributes to the real part of the
second constellation is a bit that causes the polarity of the real
part of the second constellation to be reversed, for example, when
the value of such a bit is reversed from 0 to 1 or from 1 to 0.
Stated differently, the bit that most contributes to the real part
of the second constellation refers to a bit that causes the
negative/positive sign of the value of the real part of each
modulated symbol to be reversed, for example, when the value of
such a bit is reversed from 0 to 1 or from 1 to 0.
[0389] In the above description, mapper 1423 converts the second
bit stream, thereby substantially converting the second mapping
scheme (the second constellation). However, mapper 1423 may
directly convert the second mapping scheme (the second
constellation) without converting the second bit stream. Stated
differently, mapper 1423 may convert the correspondence between
groups of bits and signal points in the second constellation.
[0390] Also, the conversion performed by mapper 1423 may be
performed by the converter included in mapper 1423.
[0391] As described above, the polarity of the real part of each
second modulated symbol is controlled in accordance with the values
of the bits to be mapped onto the first modulated symbol that is
superposed with such a second modulated symbol. Note that the
polarity of the real part of each second modulated symbol may be
controlled in accordance with the first modulated symbol that is
superposed with such a second modulated symbol.
[0392] In the above, superposition coding is performed on the real
part. Accordingly, a first modulated symbol is constituted by a
real component, and the real component of the first modulated
symbol and the real component of a second modulated symbol are
superposed on a single real component. However, superposition
coding may be performed on the imaginary part. Accordingly, a first
modulated symbol may be constituted by an imaginary component, and
the imaginary component of the first modulated symbol and the
imaginary component of a second modulated symbol may be superposed
on a single imaginary component.
<Sequential Decoding of Signal Obtained by Variation of
Superposition Coding>
[0393] FIG. 27 shows an example configuration of reception device
1500 capable of receiving and sequentially decoding the signal on
which two data series are multiplexed onto two layers by the
above-described variation of superposition coding, and capable of
obtaining one of or both of the multiplexed two data series. The
configuration and operation of reception device 1500 will be
described with reference to FIG. 27.
[0394] Reception device 1500 includes RF unit 1530, demapper 1511,
deinterleaver 1512, decoder 1513, encoder 1514, interleaver 1515,
mapper 1516, multiplier 1517, delayer 1518, subtractor 1519,
converter 1520, demapper 1521, deinterleaver 1522, and decoder
1523. These structural components may also be implemented as
dedicated or general-purpose circuits.
[0395] Demapper 1511, deinterleaver 1512, decoder 1513, encoder
1514, interleaver 1515, mapper 1516, multiplier 1517, delayer 1518,
subtractor 1519, converter 1520, demapper 1521, deinterleaver 1522,
and decoder 1523 can also be represented collectively as a deriver.
RF unit 1530 can also be represented as a receiver. RF unit 1530
may include an antenna.
[0396] Reception device 1500 receives by an antenna the multiplexed
signal sent from transmission device 1200, 1300, or 1400, and
inputs such a multiplexed signal into RF unit 1530. Stated
differently, RF unit 1530 receives the multiplexed signal via the
antenna. The multiplexed signal received by RF unit 1530 is also
represented as a received signal, and corresponds to the superposed
modulated symbol stream into which the first modulated symbol
stream and the second modulated symbol stream are multiplexed. RF
unit 1530 generates a baseband received signal from the
radio-frequency received signal.
[0397] Demapper 1511 demaps the baseband received signal on the
basis of the first constellation of the first mapping scheme to
generate the first bit likelihood stream. For example, amplitude
coefficient a.sub.1 is reflected in the first constellation for
demapping.
[0398] Deinterleaver 1512 permutes the first bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
first permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1513 performs decoding that is based on the
first error control coding scheme by use of the first bit
likelihood stream permuted by deinterleaver 1512, and outputs the
decoding result as the first data series.
[0399] Here, of the received signal corresponding to the superposed
modulated symbol stream, demapper 1511 treats the components
corresponding to the second modulated symbols in the second data
series as an unknown signal (noise), and performs demapping on the
basis of the first constellation of the first mapping scheme.
[0400] When only the first data series is to be obtained, reception
device 1500 terminates the process upon completing the estimation
of the first data series. Meanwhile, when the second data series is
to be obtained in addition to the first data series, or when only
the second data series is to be obtained, reception device 1500
performs the processes described below to obtain the second data
series.
[0401] Encoder 1514 encodes the first data series obtained by
decoder 1513 on the basis of the first error control coding scheme
to generate the first bit stream. Interleaver 1515 permutes the
bits in the first bit stream generated by encoder 1514 on the basis
of the first permutation rule. Such permutation is also referred to
as interleaving.
[0402] Mapper 1516 maps the first bit stream permuted by
interleaver 1515 in accordance with the first mapping scheme to
generate the first modulated symbol stream that includes a
plurality of first modulated symbols. Multiplier 1517 multiplies
the first modulated symbol stream outputted by mapper 1516 by first
amplitude coefficient a.sub.1.
[0403] Delayer 1518 delays the received signal outputted from RF
unit 1530 during the time from when RF unit 1530 outputs the
baseband received signal to when multiplier 1517 outputs the
reproduced first modulated symbol stream.
[0404] Subtractor 1519 subtracts, from the received signal delayed
by delayer 1518, the first modulated symbol stream multiplied by
first amplitude coefficient a.sub.1 by multiplier 1517. Through
this, subtractor 1519 removes the components corresponding to the
first modulated symbols from the received signal on which the
components corresponding to the first modulated symbols, the
components corresponding to the second modulated symbols, and noise
are superposed. Subsequently, subtractor 1519 outputs a signal on
which the components corresponding to the second modulated symbols
and noise are superposed as a signal corresponding to the second
modulated symbol stream.
[0405] Converter 1520 converts the signal outputted from subtractor
1519 as a signal corresponding to the second modulated symbol
stream by use of the first bit stream reproduced through encoding,
interleaving, etc. Demapper 1521 demaps the signal outputted by
converter 1520 on the basis of the second constellation of the
second mapping scheme to generate the second bit likelihood stream.
For example, amplitude coefficient a.sub.2 is reflected in the
second constellation for demapping.
[0406] Deinterleaver 1522 permutes the second bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
second permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1523 decodes the second bit likelihood
stream permuted by deinterleaver 1522 on the basis of the second
error control coding scheme, and outputs the decoding result as the
second data series.
[0407] The following shows an example case in which BPSK is used as
the first mapping scheme to describe the operation of converter
1520.
[0408] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 1516, and
b.sub.1(t) is a bit to be mapped onto S.sub.1(t), modulated symbol
S.sub.1(t) is given by Equation 21.
[Math. 21]
S.sub.1(t)=2b.sub.1(t)-1 (Equation 21)
[0409] Modulated symbol S.sub.1(t) may also be given by an equation
in which the polarity in Equation 21 is reversed. Converter 1520
converts, into S'.sub.2(t), signal S.sub.2(t) corresponding to the
t-th modulated symbol in the second modulated symbol stream among
signals outputted by subtractor 1519, on the basis of b.sub.1(t) as
shown by Equation 22.
[Math. 22]
S'.sub.2(t)=(-1).sup.b.sup.1.sup.(t)Re[S.sub.2(t)]+iIm[S.sub.2(t)]
(Equation 22)
[0410] Here, i denotes the imaginary unit. Further, S'.sub.2(t) is
the signal that has undergone the conversion. Also, Re[S.sub.2(t)]
is the value of the real part of S.sub.2(t), and Im[S.sub.2(t)] is
the value of the imaginary part of S.sub.2(t). Signal S'.sub.2(t)
that has undergone the conversion may be given by an equation in
which one of or both of the polarities of the real part and the
imaginary part of Equation 22 are reversed.
[0411] Through the above processes, reception device 1500 obtains
one of or both of the first data series and the second data series
from the signal received by the antenna. Note that in the above,
superposition coding is performed on the real part. However,
superposition coding may be performed on the imaginary part.
[0412] FIG. 28 shows an example configuration of reception device
1600 capable of receiving and sequentially decoding the signal on
which two data series are multiplexed onto two layers by the
above-described variation of superposition coding, and capable of
obtaining one of or both of the multiplexed two data series. The
configuration of reception device 1600 is different from the
configuration of reception device 1500. The configuration and
operation of reception device 1600 will be described with reference
to FIG. 28.
[0413] Reception device 1600 includes RF unit 1630, demapper 1611,
deinterleaver 1612, decoder 1613, encoder 1614, interleaver 1615,
mapper 1616, multiplier 1617, delayer 1618, subtractor 1619,
converter 1620, demapper 1621, deinterleaver 1622, and decoder
1623. These structural components may also be implemented as
dedicated or general-purpose circuits.
[0414] Demapper 1611, deinterleaver 1612, decoder 1613, encoder
1614, interleaver 1615, mapper 1616, multiplier 1617, delayer 1618,
subtractor 1619, converter 1620, demapper 1621, deinterleaver 1622,
and decoder 1623 can also be represented collectively as a deriver.
RF unit 1630 can also be represented as a receiver. RF unit 1630
may include an antenna.
[0415] Reception device 1600 receives by an antenna the multiplexed
signal sent from transmission device 1200, 1300, or 1400, and
inputs such a multiplexed signal into RF unit 1630. Stated
differently, RF unit 1630 receives the multiplexed signal via the
antenna. The multiplexed signal received by RF unit 1630 is also
represented as a received signal, and corresponds to the superposed
modulated symbol stream into which the first modulated symbol
stream and the second modulated symbol stream are multiplexed. RF
unit 1630 generates a baseband received signal from the
radio-frequency received signal.
[0416] Demapper 1611 demaps the baseband received signal on the
basis of the first constellation of the first mapping scheme to
generate the first bit likelihood stream. For example, amplitude
coefficient a.sub.1 is reflected in the first constellation for
demapping.
[0417] Deinterleaver 1612 permutes the first bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
first permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1613 performs decoding that is based on the
first error control coding scheme by use of the first bit
likelihood stream permuted by deinterleaver 1612, and outputs the
decoding result as the first data series.
[0418] Here, of the received signal corresponding to the superposed
modulated symbol stream, demapper 1611 treats the components
corresponding to the second modulated symbols in the second data
series as an unknown signal (noise), and performs demapping on the
basis of the first constellation of the first mapping scheme.
[0419] When only the first data series is to be obtained, reception
device 1600 terminates the process upon completing the estimation
of the first data series. Meanwhile, when the second data series is
to be obtained in addition to the first data series, or when only
the second data series is to be obtained, reception device 1600
performs the processes described below to obtain the second data
series.
[0420] Encoder 1614 encodes the first data series obtained by
decoder 1613 on the basis of the first error control coding scheme
to generate the first bit stream. Interleaver 1615 permutes the
bits in the first bit stream generated by encoder 1614 on the basis
of the first permutation rule. Such permutation is also referred to
as interleaving.
[0421] Mapper 1616 maps the first bit stream permuted by
interleaver 1615 in accordance with the first mapping scheme to
generate the first modulated symbol stream that includes a
plurality of first modulated symbols. Multiplier 1617 multiplies
the first modulated symbol stream outputted by mapper 1616 by first
amplitude coefficient a.sub.1.
[0422] Delayer 1618 delays the received signal outputted from RF
unit 1630 during the time from when RF unit 1630 outputs the
baseband received signal to when multiplier 1617 outputs the
reproduced first modulated symbol stream.
[0423] Subtractor 1619 subtracts, from the received signal delayed
by delayer 1618, the first modulated symbol stream multiplied by
first amplitude coefficient a.sub.1 by multiplier 1617. Through
this, subtractor 1619 removes the components corresponding to the
first modulated symbols from the received signal on which the
components corresponding to the first modulated symbols and the
components corresponding to the second modulated symbols and noise
are superposed. Subsequently, subtractor 1619 outputs a signal on
which the components corresponding to the second modulated symbols
and noise are superposed as a signal corresponding to the second
modulated symbol stream.
[0424] Converter 1620 converts the signal outputted from subtractor
1619 as a signal corresponding to the second modulated symbol
stream by use of the first modulated symbol stream reproduced
through encoding, interleaving, mapping, etc. Demapper 1621 demaps
the signal outputted by converter 1620 on the basis of the second
constellation of the second mapping scheme to generate the second
bit likelihood stream. For example, amplitude coefficient a.sub.2
is reflected in the second constellation for demapping.
[0425] Deinterleaver 1622 permutes the second bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
second permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1623 decodes the second bit likelihood
stream permuted by deinterleaver 1622 on the basis of the second
error control coding scheme, and outputs the decoding result as the
second data series.
[0426] The following shows an example case in which BPSK is used as
the first mapping scheme to describe the operation of converter
1620.
[0427] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 1616, and
b.sub.1(t) is a bit to be mapped onto S.sub.1(t), modulated symbol
S.sub.1(t) is given by Equation 23.
[Math. 23]
S.sub.1(t)=2b.sub.1(t)-1 (Equation 23)
[0428] Modulated symbol S.sub.1(t) may also be given by an equation
in which the polarity in Equation 23 are reversed. Converter 1620
converts, into S'.sub.2(t), signal S.sub.2(t) corresponding to the
t-th modulated symbol in the second modulated symbol stream out of
the signal outputted by subtractor 1619, on the basis of modulated
symbol S.sub.1(t) as shown by Equation 24.
[Math. 24]
S'.sub.2(t)=-sgn(S.sub.1(t))Re[S.sub.2(t)]+iIm[S.sub.2(t)]
(Equation 24)
[0429] Here, i denotes the imaginary unit. Further, S'.sub.2(t) is
the signal that has undergone the conversion. Also, Re[S.sub.2(t)]
is the value of the real part of S.sub.2(t), and Im[S.sub.2(t)] is
the value of the imaginary part of S.sub.2(t). Also,
sgn(S.sub.1(t)) is the polarity of S.sub.1(t). Signal S'.sub.2(t)
that has undergone the conversion may be given by an equation in
which one of or both of the polarities of the real part and the
imaginary part of Equation 24 are reversed. Note that the
conversion that is based on Equation 24 is substantially the same
as the conversion that is based on Equation 22.
[0430] Through the above processes, reception device 1600 obtains
one of or both of the first data series and the second data series
from the signal received by the antenna. Note that in the above,
superposition coding is performed on the real part, but may be
performed on the imaginary part.
[0431] FIG. 29 shows an example configuration of reception device
1700 capable of receiving and sequentially decoding the signal on
which two data series are multiplexed onto two layers by the
above-described variation of superposition coding, and capable of
obtaining one of or both of the multiplexed two data series. The
configuration of reception device 1700 is different from the
configurations of reception devices 1500 and 1600. The
configuration and operation of reception device 1700 will be
described with reference to FIG. 29.
[0432] Reception device 1700 includes RF unit 1730, demapper 1711,
deinterleaver 1712, decoder 1713, encoder 1714, interleaver 1715,
mapper 1716, multiplier 1717, delayer 1718, subtractor 1719,
demapper 1721, deinterleaver 1722, and decoder 1723. These
structural components may also be implemented as dedicated or
general-purpose circuits.
[0433] Demapper 1711, deinterleaver 1712, decoder 1713, encoder
1714, interleaver 1715, mapper 1716, multiplier 1717, delayer 1718,
subtractor 1719, demapper 1721, deinterleaver 1722, and decoder
1723 can also be represented collectively as a deriver. RF unit
1730 can also be represented as a receiver. RF unit 1730 may
include an antenna. Demapper 1721 may include a converter.
[0434] Reception device 1700 receives by an antenna the multiplexed
signal sent from transmission device 1200, 1300, or 1400, and
inputs such a multiplexed signal into RF unit 1730. Stated
differently, RF unit 1730 receives the multiplexed signal via the
antenna. The multiplexed signal received by RF unit 1730 is also
represented as a received signal, and corresponds to the superposed
modulated symbol stream into which the first modulated symbol
stream and the second modulated symbol stream are multiplexed. RF
unit 1730 generates a baseband received signal from the
radio-frequency received signal.
[0435] Demapper 1711 demaps the baseband received signal on the
basis of the first constellation of the first mapping scheme to
generate the first bit likelihood stream. For example, amplitude
coefficient a.sub.1 is reflected in the first constellation for
demapping.
[0436] Deinterleaver 1712 permutes the first bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
first permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1713 performs decoding that is based on the
first error control coding scheme by use of the first bit
likelihood stream permuted by deinterleaver 1712, and outputs the
decoding result as the first data series.
[0437] Here, of the received signal corresponding to the superposed
modulated symbol stream, demapper 1711 treats the components
corresponding to the second modulated symbols in the second data
series as an unknown signal (noise), and performs demapping on the
basis of the first constellation of the first mapping scheme.
[0438] When only the first data series is to be obtained, reception
device 1700 terminates the process upon completing the estimation
of the first data series. Meanwhile, when the second data series is
to be obtained in addition to the first data series, or when only
the second data series is to be obtained, reception device 1700
performs the processes described below to obtain the second data
series.
[0439] Encoder 1714 encodes the first data series obtained by
decoder 1713 on the basis of the first error control coding scheme
to generate the first bit stream. Interleaver 1715 permutes the
bits in the first bit stream generated by encoder 1714 on the basis
of the first permutation rule. Such permutation is also referred to
as interleaving.
[0440] Mapper 1716 maps the first bit stream permuted by
interleaver 1715 in accordance with the first mapping scheme to
generate the first modulated symbol stream that includes a
plurality of first modulated symbols. Multiplier 1717 multiplies
the first modulated symbol stream outputted by mapper 1716 by first
amplitude coefficient a.sub.1.
[0441] Delayer 1718 delays the received signal outputted from RF
unit 1730 during the time from when RF unit 1730 outputs the
baseband received signal to when multiplier 1717 outputs the
reproduced first modulated symbol stream.
[0442] Subtractor 1719 subtracts, from the received signal delayed
by delayer 1718, the first modulated symbol stream multiplied by
first amplitude coefficient a.sub.1 by multiplier 1717. Through
this, subtractor 1719 removes the components corresponding to the
first modulated symbols from the received signal on which the
components corresponding to the first modulated symbols, the
components corresponding to the second modulated symbols, and noise
are superposed. Subsequently, subtractor 1719 outputs a signal on
which the components corresponding to the second modulated symbols
and noise are superposed as a signal corresponding to the second
modulated symbol stream.
[0443] Demapper 1721 demaps the signal outputted from subtractor
1719 as a signal corresponding to the second modulated symbol
stream on the basis of the second constellation of the second
mapping scheme to generate the second bit likelihood stream. At
this time, such a process reflects the first bit stream reproduced
through encoding, interleaving, etc. For example, amplitude
coefficient a.sub.2 is reflected in the second constellation for
demapping.
[0444] Deinterleaver 1722 permutes the second bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
second permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1723 decodes the second bit likelihood
stream permuted by deinterleaver 1722 on the basis of the second
error control coding scheme, and outputs the decoding result as the
second data series.
[0445] The following shows an example case in which BPSK is used as
the first mapping scheme to describe the operation of demapper
1721.
[0446] For example, when S.sub.1(t) is the t-th modulated symbol in
the first modulated symbol stream generated by mapper 1716, and
b.sub.1(t) is a bit to be mapped onto S.sub.1(t), modulated symbol
S.sub.1(t) is given by Equation 25.
[Math. 25]
S.sub.1(t)=2b.sub.1(t)-1 (Equation 25)
[0447] Modulated symbol S.sub.1(t) may also be given by an equation
in which the polarity in Equation 25 is reversed. Demapper 1721
demaps signal S.sub.2(t) outputted from subtractor 1719 as a signal
corresponding to the t-th modulated symbol in the second modulated
symbol stream on the basis of the second constellation of the
second mapping scheme.
[0448] Demapper 1721 reverses the bit likelihood corresponding to
the bit that most contributes to the real part of the second
constellation in accordance with b.sub.1(t) among the bit
likelihoods in the bit likelihood stream obtained by demapping. For
example, demapper 1721 performs exclusive-OR between b.sub.1(t) and
the bit likelihood corresponding to the bit that most contributes
to the real part of the second constellation among the bit
likelihoods in the bit likelihood stream obtained by demapping.
[0449] Demapper 1721 then outputs the bit likelihood stream that
has undergone the above-described reversal processes as the second
bit likelihood stream.
[0450] In the above description, demapper 1721 converts the bit
likelihood stream, thereby substantially converting the second
mapping scheme (the second constellation). However, demapper 1721
may directly convert the second mapping scheme (the second
constellation) without converting the bit likelihood stream. Stated
differently, demapper 1721 may convert the correspondence between
groups of bits and signal points in the second constellation.
[0451] Also, the conversion performed by demapper 1721 may be
performed by the converter included in demapper 1721.
[0452] Through the above processes, reception device 1700 obtains
one of or both of the first data series and the second data series
from the signal received by the antenna. Note that in the above,
superposition coding is performed on the real part. However,
superposition coding may be performed on the imaginary part.
<Parallel Decoding of Signal Obtained by Variation of
Superposition Coding>
[0453] The following describes a reception method for parallel
decoding of a signal obtained by the variation of superposition
coding according to the present embodiment. The configuration of
the transmission device is the same as the configuration of
transmission device 1200 shown in FIG. 24, transmission device 1300
shown in FIG. 25, or transmission device 1400 shown in FIG. 26, and
thus will not be described. In parallel decoding in the variation
of superposition coding, the reception device treats the components
of the modulated symbol stream in the first layer as an unknown
signal (noise) to decode the second layer, without removing the
components of the modulated symbol stream in the first layer
included in the received signal.
[0454] FIG. 30 shows an example configuration of reception device
1800 capable of receiving and performing parallel decoding on the
signal on which two data series are multiplexed onto two layers by
the variation of superposition coding, and capable of obtaining one
of or both of the multiplexed two data series. The configuration
and operation of reception device 1800 will be described with
reference to FIG. 30.
[0455] Reception device 1800 includes RF unit 1830, demapper 1810,
deinterleaver 1812, decoder 1813, deinterleaver 1822, and decoder
1823. These structural components may also be implemented as
dedicated or general-purpose circuits. Demapper 1810, deinterleaver
1812, decoder 1813, deinterleaver 1822, and decoder 1823 can also
be represented collectively as a deriver. RF unit 1830 can also be
represented as a receiver. RF unit 1830 may include an antenna.
[0456] Reception device 1800 receives by an antenna the multiplexed
signal sent from transmission device 1200, 1300, or 1400, and
inputs such a multiplexed signal into RF unit 1830. Stated
differently, RF unit 1830 receives the multiplexed signal via the
antenna. The multiplexed signal received by RF unit 1830 can also
be represented as a received signal. RF unit 1830 generates a
baseband received signal from the radio-frequency received
signal.
[0457] Demapper 1810 demaps the baseband received signal to
generate the first bit likelihood stream and the second bit
likelihood stream. For example, demapper 1810 performs demapping on
the basis of a variation superposition constellation that shows the
arrangement of signal points of superposed modulated symbols
obtained by superposing the first modulated symbols and the second
modulated symbols by the variation of superposition coding.
[0458] The variation superposition constellation is determined in
accordance with the first constellation of the first mapping
scheme, the second constellation of the second mapping scheme,
first amplitude coefficient a.sub.1, second amplitude coefficient
a.sub.2, etc.
[0459] FIG. 31 shows an example of a BPSK constellation. More
specifically, two BPSK signal points are plotted in the complex
plane, with the lateral axis representing the real part (the real
component) and the vertical axis representing the imaginary part
(the imaginary component). Note that BPSK means binary phase shift
keying.
[0460] For example, in BPSK, a bit (0 or 1) is associated with a
modulated symbol indicating a complex number on the basis of the
constellation shown in FIG. 31. In this example, a bit is
associated with a modulated symbol indicating a complex number
whose imaginary part is 0. Specifically, in this example, a bit is
substantially associated with a modulated symbol indicating a real
number.
[0461] FIG. 32 shows the variation superposition constellation that
supports the variation of superposition coding. More specifically,
the variation superposition constellation is a combination of the
BPSK constellation shown in FIG. 31 and the Nu-256QAM constellation
shown in FIG. 5.
[0462] Even more specifically, the Nu-256QAM constellation (256
signal points) is placed on each of two regions in the complex
plane in accordance with the two signal points of the BPSK
constellation. These two regions, each corresponding to Nu-256QAM
constellation, may partially overlap with each other. The present
variation superposition constellation reflects the conversion
performed on the second modulated symbol stream.
[0463] For example, when the Nu-256QAM constellation is combined
with a signal point with a positive real part among the two signal
points of the BPSK constellation, the polarity of the real part of
the Nu-256QAM constellation is reversed. More specifically, a first
signal point, a second signal point, and a third signal point are
shown in FIG. 32. When the polarity of the real part of the
Nu-256QAM constellation is not reversed, the first signal point and
the third signal point correspond to the same bit values of the
second bit stream.
[0464] When the polarity of the real part of the Nu-256QAM
constellation is reversed, the first signal point and the second
signal point correspond to the same bit values of the second bit
stream. Stated differently, such reversal enables a plurality of
signal points that correspond to the same bit values of the second
bit stream to approach each other and converge. This mitigates the
effect of noise on demapping.
[0465] Demapper 1810 performs demapping on the basis of the
variation superposition constellation as shown in FIG. 32. Stated
differently, demapper 1810 generates the first bit likelihood
stream with the modulated symbol stream of the second layer
remaining unknown, and generates the second bit likelihood stream
with the modulated symbol stream of the first layer remaining
unknown.
[0466] Note that demapper 1810 may use the first constellation of
the first mapping scheme to generate the first bit likelihood
stream, and may use the above-described variation superposition
constellation to generate the second bit likelihood stream.
[0467] The first constellation, when used to generate the first bit
likelihood stream, enables demapper 1810 to reduce the number of
signal points that should be considered in generating the first bit
likelihood stream, compared to when the variation superposition
constellation is also used to generate the first bit likelihood
stream. This thus enables demapper 1810 to reduce the number of
arithmetic computations.
[0468] Demapper 1810 corresponds, for example, to the first
demapper that demaps the received signal to generate the first bit
likelihood stream and the second demapper that demaps the received
signal to generate the second bit likelihood stream. Demapper 1810
may include the first demapper that demaps the received signal to
generate the first bit likelihood stream and the second demapper
that demaps the received signal to generate the second bit
likelihood stream.
[0469] Demapper 1810 may convert the second bit likelihood stream
that is generated using not the variation superposition
constellation but the superposition constellation, in accordance
with the first bit likelihood stream. This enables demapper 1810 to
obtain the same second bit likelihood stream as the second bit
likelihood stream that is generated using the variation
superposition constellation.
[0470] Demapper 1810 may convert the multiplexed signal without
using the variation superposition constellation to obtain the same
second bit likelihood stream as the second bit likelihood stream
that is generated using the variation superposition
constellation.
[0471] Deinterleaver 1812 permutes the first bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
first permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1813 decodes the first bit likelihood
stream permuted by deinterleaver 1812 on the basis of the first
error control coding scheme, and outputs the decoding result as the
first data series.
[0472] Deinterleaver 1822 permutes the second bit likelihood stream
on the basis of a permutation rule that is a reverse rule of the
second permutation rule. Such permutation is also referred to as
deinterleaving. Decoder 1823 decodes the second bit likelihood
stream permuted by deinterleaver 1822 on the basis of the second
error control coding scheme, and outputs the decoding result as the
second data series.
[0473] Through the above processes, reception device 1800 obtains
one of or both of the first data series and the second data series
from the signal received by the antenna. Note that in the above,
superposition coding is performed on the real part. However,
superposition coding may be performed on the imaginary part.
[0474] Note that transmission devices 1200, 1300, and 1400, and
reception devices 1500, 1600, 1700, and 1800 may omit permutation
(interleaving and deinterleaving) as in the case of Embodiment 1.
Stated differently, their respective interleavers and
deinterleavers are optional structural components, and thus may not
be included in these devices.
[0475] Interleaving and deinterleaving, however, make a pair. As
such, when transmission devices 1200, 1300, and 1400 include their
respective interleavers, reception devices 1500, 1600, 1700, and
1800 basically include their respective deinterleavers and
interleavers. Meanwhile, when transmission devices 1200, 1300, and
1400 do not include their respective interleavers, reception
devices 1500, 1600, 1700, and 1800 do not include their respective
deinterleavers and interleavers.
[0476] Amplitude coefficient a.sub.1 may be reflected in the
mapping for generating the first modulated symbols performed in
reception devices 1500, 1600, and 1700. In such a case, the
multiplication of amplitude coefficient a.sub.1 may be omitted.
Reception devices 1500, 1600, and 1700 thus may not include
multipliers 1517, 1617, and 1717, respectively.
[0477] Error control coding on the first data series and the second
data series may be performed by an external device. In such a case,
transmission devices 1200, 1300, and 1400 may omit error control
coding, and may not include encoders 1211, 1221, 1311, 1321, 1411,
and 1421.
[0478] As described above, superposition coding may be performed on
the real part or on the imaginary part. Furthermore, superposition
coding may be performed in a predetermined direction in the complex
plane. For example, superposition coding may be performed in an
oblique direction in an orthogonal coordinate system having a real
axis and an imaginary axis.
[0479] Specifically, a first modulated symbol may include a
component in the first direction in the complex plane, and a second
modulated symbol may include a component in the first direction and
a component in the second direction perpendicular to the first
direction. The component that a first modulated symbol includes in
the first direction and the component that a second modulated
symbol includes in the first direction may be superposed on a
single component in the first direction. In this case, for example,
the polarity of the component of the second modulated symbol in the
first direction is controlled in accordance with the component of
the first modulated symbol in the first direction.
[0480] Specifically, in the description given herein, a real
component may be replaced with an imaginary component, replaced
with a component in the first direction that is one direction in
the complex plane, or replaced with a component in the second
direction perpendicular to the first direction. In addition, an
imaginary component may be replaced with a real component, replaced
with a component in the first direction that is one direction in
the complex plane, or replaced with a component in the second
direction perpendicular to the first direction.
[0481] For example, a component that a modulated symbol includes in
the first direction includes a real part and an imaginary part, and
the polarity of such a component is reversed, thus reversing both
of the polarities of the real and imaginary parts of the component.
Furthermore, the polarity of the component may be determined in
accordance with the polarity of the real part of the component or
in accordance with the polarity of the imaginary part of the
component.
[0482] Specifically, when the polarity of the real part of the
component is positive, the polarity of the component may be
determined to be positive, and when the polarity of the real part
of the component is negative, the polarity of the component may be
determined to be negative. Alternatively, when the polarity of the
imaginary part of the component is positive, the polarity of the
component may be determined to be positive, and when the polarity
of the imaginary part of the component is negative, the polarity of
the component may be determined to be negative.
[0483] Furthermore, the direction of the real axis may be the first
direction or may be the second direction perpendicular to the first
direction. The direction of the imaginary axis may be the first
direction or may be the second direction perpendicular to the first
direction.
[0484] The first constellation of the first mapping scheme may have
a plurality of signal points dispersed in only the first direction.
Furthermore, the second constellation of the second mapping scheme
may have a plurality of signal points dispersed in both the first
direction and the second direction.
[0485] The first mapping scheme is not limited to BPSK. A
constellation having three or more signal points may be used as the
first constellation of the first mapping scheme. For example, a
constellation having three or more signal points on a straight line
in the complex plane may be used as the first constellation of the
first mapping scheme.
[0486] In the first constellation of the first mapping scheme, the
polarity in the first direction of the second mapping scheme is
reversed for two signal points adjacent to each other along a
straight line in the first direction. Specifically, the polarity is
reversed such that a second modulated symbol superposed on a first
modulated symbol corresponding to one of the two signal points and
a second modulated symbol superposed on a first modulated symbol
corresponding to the other have different polarities in the first
direction. Thus, the polarities in the first direction are
alternated along a sequence of three or more signal points on a
straight line in the first direction.
[0487] FIG. 33 is a flowchart of example operations performed by
transmission device 1200. First, mapper 1213 maps the first bit
stream of the first data series to generate the first modulated
symbol stream of the first data series (S501). Then, mapper 1223
maps the second bit stream of the second data series to generate
the second modulated symbol stream of the second data series
(S502).
[0488] Converter 1225 subjects the second modulated symbol stream
to conversion in accordance with the first modulation symbol
stream, in only the first direction among the first direction and
the second direction (S503). Here, the first direction and the
second direction are two directions perpendicular to each other in
the complex plane in which the first modulated symbol stream and
the second modulated symbol stream are represented.
[0489] Specifically, converter 1225 does not subject a component
that the second modulated symbol stream includes in the second
direction to conversion in accordance with the first modulation
symbol stream, but subjects a component that the second modulated
symbol stream includes in the first direction to the conversion.
Furthermore, converter 1225 converts the second modulated symbol
stream in accordance with the first bit stream, thereby subjecting
the second modulated symbol stream to conversion in accordance with
the first modulated symbol stream.
[0490] Next, the superposer superposes the first modulated symbol
stream and the second modulated symbol stream that has been
subjected to conversion in accordance with the first modulated
symbol stream at a predetermined amplitude ratio, thereby
generating the multiplexed signal (S504). Here, the superposer is
constituted by first multiplier 1214, second multiplier 1224, and
adder 1230. RF unit 1240 then sends the generated multiplexed
signal (S505).
[0491] Note that in the above operation example, transmission
device 1200 converts the second modulated symbol stream in
accordance with the first bit stream, thereby subjecting the second
modulated symbol stream to conversion in accordance with the first
modulated symbol stream (S503). Alternatively, transmission device
1200 may convert the second modulated symbol stream in accordance
with the first modulated symbol stream, as in the case of
transmission device 1300, thereby subjecting the second modulated
symbol stream to conversion in accordance with the first modulated
symbol stream.
[0492] Alternatively, as in the case of transmission device 1400,
transmission device 1200 may convert the second bit stream or the
second mapping scheme (the second constellation) used to generate
the second modulated symbol stream, in accordance with the first
bit stream. Through this, the second modulated symbol stream may be
subjected to conversion in accordance with the first modulated
symbol stream. In such a case, the second bit stream or the second
mapping scheme is converted before the second modulated symbol
stream is generated.
[0493] Stated differently, the second bit stream, the second
mapping scheme, or the second modulated symbol stream may be
converted in accordance with the first bit stream or the first
modulated symbol stream, thereby subjecting the second modulated
symbol stream to conversion in accordance with the first modulated
symbol stream.
[0494] Converter 1225 may subject the second modulated symbol
stream to conversion in accordance with the first modulated symbol
stream, thereby controlling the polarity of a component that each
modulated symbol in the second modulated symbol stream includes in
the first direction. Through this, converter 1225 may reverse the
polarity of a component that each second modulated symbol includes
in the first direction when a component that the corresponding
first modulated symbol includes in the first direction satisfies a
predetermined condition.
[0495] The predetermined condition may be a condition that the
polarity of a component that the first modulated symbol includes in
the first direction should be a predetermined polarity, or may be a
condition that the component that the first modulated symbol
includes in the first direction should be within a predetermined
range of one or more. The predetermined range of one or more may be
a positive range or a negative range.
[0496] FIG. 34 is a flowchart of example operations performed by
reception devices 1500, 1600, 1700, and 1800. First, the receiver
receives the multiplexed signal (S601). Here, the receiver is RF
unit 1530 of reception device 1500, RF unit 1630 of reception
device 1600, RF unit 1730 of reception device 1700, or RF unit 1830
of reception device 1800.
[0497] The multiplexed signal is a signal into which a plurality of
data series including the first data series in the first layer and
the second data series in the second layer are multiplexed. The
multiplexed signal is also a signal on which the first modulated
symbol stream and the second modulated symbol stream are superposed
at a predetermined amplitude ratio.
[0498] The first modulated symbol stream is a modulated symbol
stream that is generated by mapping the first bit stream of the
first data series. The second modulated symbol stream is a
modulated symbol stream that is generated by mapping the second bit
stream of the second data series, and that has been subjected to
conversion in accordance with the first modulated symbol stream in
only the first direction among the first direction and the second
direction in a complex plane.
[0499] Next, the deriver derives at least one of the first data
series or the second data series from the multiplexed signal
(S602).
[0500] The deriver of reception device 1500 is constituted, for
example, by demapper 1511, deinterleaver 1512, decoder 1513,
encoder 1514, interleaver 1515, mapper 1516, multiplier 1517,
delayer 1518, subtractor 1519, converter 1520, demapper 1521,
deinterleaver 1522, and decoder 1523.
[0501] The deriver of reception device 1600 is constituted, for
example, by demapper 1611, deinterleaver 1612, decoder 1613,
encoder 1614, interleaver 1615, mapper 1616, multiplier 1617,
delayer 1618, subtractor 1619, converter 1620, demapper 1621,
deinterleaver 1622, and decoder 1623.
[0502] The deriver of reception device 1700 is constituted, for
example, by demapper 1711, deinterleaver 1712, decoder 1713,
encoder 1714, interleaver 1715, mapper 1716, multiplier 1717,
delayer 1718, subtractor 1719, demapper 1721, deinterleaver 1722,
and decoder 1723.
[0503] The deriver of reception device 1800 is constituted, for
example, by demapper 1810, deinterleaver 1812, decoder 1813,
deinterleaver 1822, and decoder 1823.
[0504] In accordance with the above operations, the multiplexed
signal is received into which the first modulated symbol stream and
the second modulated symbol stream that has been subjected to
conversion in accordance with the first modulated symbol stream in
the first direction are multiplexed. Then, at least one of the
first data series or the second data series is derived from such a
multiplexed signal. Stated differently, such a configuration
enables: the reception of the multiplexed signal that has been
superposed in such a manner that reduces performance degradation at
the time of parallel decoding: and an efficient derivation of one
of or both of the first data series and the second data series from
such a multiplexed signal.
[0505] Reception device 1800 as shown in FIG. 30 that performs
parallel decoding has lower performance in decoding the second
layer than that of reception devices 1500, 1600, and 1700 as shown
in FIG. 27, FIG. 28, and FIG. 29 that perform sequential
decoding.
[0506] As described above, reception device 1800 according to the
present embodiment that performs parallel decoding has lower
performance in decoding the second data series transmitted on the
second layer than that of reception devices 1500, 1600, and 1700
that perform sequential decoding. However, reception device 1800
reduces the number of structural components required to decode the
second layer.
[0507] More specifically, reception device 1800 eliminates the need
for the structural components that are required by reception
devices 1500, 1600, and 1700 shown in FIG. 27, FIG. 28, and FIG. 29
performing sequential decoding to reproduce the modulated symbol
stream of the first layer. Stated differently, encoders 1514, 1614,
and 1714, interleavers 1515, 1615, and 1715, mappers 1516, 1616,
and 1716, and multipliers 1517, 1617, and 1717 are not
required.
[0508] Reception device 1800 also eliminates the need for delayers
1518, 1618, and 1718 that delay the received signal, and
subtractors 1519, 1619, and 1719 that remove the components of the
modulated symbols in the first layer reproduced from the received
signal.
[0509] The circuit size can be thus reduced. Reception device 1800
also requires a smaller number of arithmetic computations and lower
power consumption than those required by reception devices 1500,
1600, and 1700.
[0510] Reception devices 1500, 1600, and 1700 shown in FIG. 27,
FIG. 28, and FIG. 29 that perform sequential decoding demodulate
the first layer in the received signal to obtain the first data
series, and generate the first modulated symbol stream from the
obtained first data series. Subsequently, reception devices 1500,
1600, and 1700 start demodulating the second layer in the received
signal to obtain the second data series.
[0511] Meanwhile, reception device 1800 according to the present
embodiment that performs parallel decoding is capable of
simultaneously obtaining the first data series and the second data
series in parallel, thereby reducing processing delays.
[0512] The reception device may observe the SNR of the received
signal to make selection between parallel decoding to be performed
when the SNR is high and sequential decoding to be performed when
the SNR is low.
[0513] In such a case, reception device 1500 shown in FIG. 27
includes, for example, a controller that makes selection between
sequential decoding and parallel decoding depending on the SNR.
Such a controller may be included in RF unit 1530 or demapper 1521.
Furthermore, demapper 1521 is configured to perform demapping based
on the variation superposition constellation, which is described as
an operation performed by demapper 1810 shown in FIG. 30, in
addition to demapping that is based on the second
constellation.
[0514] Demapper 1521 switches between demapping to be performed on
the signal outputted from converter 1520 on the basis of the second
constellation and demapping to be performed on the signal outputted
from RF unit 1530 on the basis of the variation superposition
constellation. For example, demapper 1521 switches between these
demapping operations in accordance with a control signal from the
controller.
[0515] Note that such a configuration is also obtained by a
combination of reception device 400 shown in FIG. 11, reception
device 1500 (converter 1520, demapper 1521, etc.) shown in FIG. 27,
and reception device 1800 (demapper 1810, etc.) shown in FIG.
30.
[0516] Another configuration is that reception device 1600 shown in
FIG. 28 includes, for example, a controller that makes selection
between sequential decoding and parallel decoding depending on the
SNR. Such a controller may be included in RF unit 1630 or demapper
1621. Furthermore, demapper 1621 is configured to perform demapping
based on the variation superposition constellation, which is
described as an operation performed by demapper 1810 shown in FIG.
30, in addition to demapping that is based on the first bit stream
and the second constellation.
[0517] Demapper 1621 switches between demapping to be performed on
the signal outputted from converter 1620 on the basis of the second
constellation and demapping to be performed on the signal outputted
from RF unit 1630 on the basis of the variation superposition
constellation. For example, demapper 1621 switches between these
demapping operations in accordance with a control signal from the
controller.
[0518] Note that such a configuration is also obtained by a
combination of reception device 400 shown in FIG. 11, reception
device 1600 (converter 1620, demapper 1621, etc.) shown in FIG. 28,
and reception device 1800 (demapper 1810, etc.) shown in FIG.
30.
[0519] Still another configuration is that reception device 1700
shown in FIG. 29 includes, for example, a controller that makes
selection between sequential decoding and parallel decoding
depending on the SNR. Such a controller may be included in RF unit
1730 or demapper 1721. Furthermore, demapper 1721 is configured to
perform demapping based on the variation superposition
constellation, which is described as an operation performed by
demapper 1810 shown in FIG. 30, in addition to demapping that is
based on the first bit stream and the second constellation.
[0520] Demapper 1721 switches between demapping to be performed on
the signal outputted from subtractor 1719 on the basis of the
second constellation and demapping to be performed on the signal
outputted from RF unit 1730 on the basis of the variation
superposition constellation. For example, demapper 1721 switches
between these demapping operations in accordance with a control
signal from the controller.
[0521] Note that such a configuration is also obtained by a
combination of reception device 400 shown in FIG. 11, reception
device 1700 (demapper 1721, etc.) shown in FIG. 29, and reception
device 1800 (demapper 1810, etc.) shown in FIG. 30.
[0522] As described above, reception devices 1500, 1600, and 1700
perform parallel decoding when the SNR is high, thereby reducing
the number of arithmetic computations and power consumption.
Reception devices 1500, 1600, and 1700 also perform parallel
decoding when the SNR is high, thereby reducing processing delays.
Meanwhile, reception devices 1500, 1600, and 1700 perform
sequential decoding when the SNR is low, thereby increasing the
possibility of correctly decoding the second data series.
[0523] In the present embodiment, different mapping rules may be
used for the real part and the imaginary part in the second mapping
scheme. When superposition coding is performed on the real part,
the receiving level of the real part is lower than the receiving
level of the imaginary part in the second mapping scheme.
Accordingly, in the second mapping scheme, it is better that the
noise tolerance of the real part is higher than the noise tolerance
of the imaginary part.
[0524] Accordingly, it is suitable to make the multilevel number
for mapping the real part smaller than the multilevel number for
mapping the imaginary part. A multilevel number is also referred to
as a modulation multilevel number. For example, 32-PAM may be used
to map the real part in accordance with the second mapping scheme,
and 64-PAM may be used to map the imaginary part.
[0525] When a non-uniform constellation is used as the second
constellation of the second mapping scheme, it is suitable to use a
non-uniform constellation in which the real part corresponds to an
SNR lower than that of the imaginary part. For example, non-uniform
32-PAM corresponding to an SNR of about 15 dB may be used to map
the real part in accordance with the second mapping scheme, and
non-uniform 32-PAM corresponding to an SNR of about 20 dB may be
used to map the imaginary part.
[0526] Note that 32 indicated as the multilevel number for mapping
the real part and 64 indicated as the multilevel number for mapping
the imaginary part are mere examples and may be other values. For
example, 4-PAM may be used for the real part, and 8-PAM may be used
for the imaginary part. Furthermore, 2-PAM may be used for the real
part, and 4-PAM may be used for the imaginary part. Furthermore,
2-PAM may be used for the real part, and 8-PAM may be used for the
imaginary part. Thus, a combination of any values may be used to
map the real part and the imaginary part.
[0527] The second data series may include two series. Among the two
series, a bit stream in one series is mapped on the real part, and
a bit stream in the other series may be mapped on the imaginary
part. One modulated symbol stream may be generated as the second
modulated symbol stream by mapping the two bit streams in the two
series on the real part and the imaginary part. In such a case, PAM
that can be used as a single-axis modulation scheme is effective.
Note that PAM means pulse amplitude modulation.
[0528] FIG. 35 shows an example of a constellation based on PAM.
Specifically, a plurality of signal points based on PAM are plotted
in the complex plane, with the lateral axis representing the real
part (the real component) and the vertical axis representing the
imaginary part (the imaginary component). In this example,
non-uniform 8-PAM is used for the real part and non-uniform 16-PAM
is used for the imaginary part.
[0529] The constellation shown in FIG. 35 may be used as the second
constellation of the second mapping scheme. Specifically, a
constellation in which more signal points are arranged in the
vertical axis direction corresponding to the imaginary part than in
the horizontal axis direction corresponding to the real part may be
used as the second constellation of the second mapping scheme.
[0530] FIG. 36 shows an example of the variation superposition
constellation corresponding to the variation of superposition
coding. Specifically, the constellation shown in FIG. 31 and the
constellation shown in FIG. 35 are combined. Stated differently, a
BPSK constellation and a constellation based on PAM are combined.
The first constellation of the first mapping scheme is the BPSK
constellation, and the second constellation of the second mapping
scheme is the constellation based on PAM.
[0531] More specifically, in accordance with two signal points in
the BPSK constellation, the constellation based on PAM (128 signal
points) is placed on each of two regions in the complex plane. The
two regions, each corresponding to the constellation based on PAM,
may partially overlap each other.
[0532] In this example, first amplitude coefficient a.sub.1 is a
positive square root of 0.75, second amplitude coefficient a.sub.2
is a positive square root of 0.25, and two constellations are
combined based on the amplitude coefficients. Note that in
superposition coding in this example, the imaginary part of the
second modulated symbol stream is not multiplied by second
amplitude coefficient a.sub.2, and the value of the imaginary part
at a signal point included in the second constellation that is a
constellation based on PAM is maintained.
[0533] The variation superposition constellation reflects the
conversion performed on the second modulated symbol stream. For
example, when the constellation based on PAM is combined with a
signal point with a positive real part among two signal points in
the BPSK constellation, the polarity of the real part in the
constellation based on PAM is reversed.
[0534] Note that in the above second mapping scheme, the mapping
rule for the real part and the mapping rule for the imaginary part
are based on PAM, yet the second mapping scheme may be a mapping
scheme other than this.
[0535] For example, arbitrary QAM or arbitrary non-uniform QAM
which has arrangement of signal points each with the real part and
the imaginary part both represented by PAM of an arbitrary
multilevel number may be used as the second mapping scheme. As
another example, arbitrary non-uniform QAM which has arrangement of
signal points each with the real part and the imaginary part either
or both of which are not represented by PAM may be used as the
second mapping scheme.
[0536] In this case, for example, the arrangement of signal points
each with the real part corresponding to an SNR of about 15 dB and
the imaginary part corresponding to an SNR of about 20 dB may be
used for the second mapping scheme. As another example, the
arrangement of signal points in which the greatest value of the
real components at the signal points is smaller than the greatest
value of the imaginary components at the signal points may be used
as the second mapping scheme.
[0537] In the above, superposition coding is performed on the real
part, yet processing on the real part and processing on the
imaginary part may be switched, and superposition coding may be
performed on the imaginary part. Stated differently, a first
modulated symbol may be constituted by the imaginary component, and
the imaginary component of the first modulated symbol and the
imaginary component of a second modulated symbol may be superposed
on a single imaginary component.
[0538] In addition, the second modulated symbol stream is not
necessarily subjected to conversion in accordance with the first
modulated symbol stream. Specifically, the polarity may not be
reversed, and may not need to be controlled. Even if such
conversion is not applied, simple superposition coding can be
performed along the real axis, the imaginary axis, or one direction
corresponding to another axis. Accordingly, this provides more
flexible superposition coding.
[0539] Even if conversion is not applied, superposition coding is
performed more efficiently by use of a mapping scheme or a
constellation according to the direction of superposition
coding.
[0540] As described above, a reception device according to an
aspect of the present disclosure is a reception device that
receives a multiplexed signal into which a plurality of data series
have been multiplexed by superposition coding, and derives the
plurality of data series from the multiplexed signal, the plurality
of data series including a first data series in a first layer and a
second data series in a second layer, the reception device
including: a receiver that receives the multiplexed signal; a first
demapper that demaps the multiplexed signal, with a second
modulated symbol stream of the second data series being included in
the multiplexed signal as an undetermined signal component, to
generate a first bit likelihood stream of the first data series; a
second demapper that demaps the multiplexed signal, with a first
modulated symbol stream of the first data series being included in
the multiplexed signal as an undetermined signal component, to
generate a second bit likelihood stream of the second data series;
a first decoder that performs error control decoding on the first
bit likelihood stream to derive the first data series; and a second
decoder that performs error control decoding on the second bit
likelihood stream to derive the second data series. The multiplexed
signal received by the receiver is a signal on which the first
modulated symbol stream and the second modulated symbol stream are
superposed at a predetermined amplitude ratio, the first modulated
symbol stream being generated by mapping a first bit stream of the
first data series, the second modulated symbol stream being
generated by mapping a second bit stream of the second data series
and being subjected to conversion in accordance with the first
modulated symbol stream in only a first direction among the first
direction and a second direction perpendicular to each other in a
complex plane in which the first modulated symbol stream and the
second modulated symbol stream are represented.
[0541] Accordingly, the reception device can derive the second data
series without waiting for derivation of the first data series, for
instance. The reception device can thus reduce processing delays.
Stated differently, the reception device can efficiently perform
processing in a multiplexing scheme that utilizes superposition
coding.
[0542] The reception device can receive the multiplexed signal into
which the first modulated symbol stream, and the second modulated
symbol stream adjusted in accordance with the first modulated
symbol stream with respect to the first direction in the complex
plane. Accordingly, the reception device can appropriately derive
the first data series and the second data series from the
multiplexed signal into which the first data series and the second
data series are appropriately multiplexed.
[0543] For example, the multiplexed signal received by the receiver
may be a signal on which a first modulated symbol in the first
modulated symbol stream and a second modulated symbol in the second
modulated symbol stream are superposed, and in which a polarity of
a component that the second modulated symbol includes in the first
direction is subjected to a reversal when a component that the
first modulated symbol includes in the first direction satisfies a
predetermined condition.
[0544] Accordingly, the reception device can receive, as a
multiplexed signal, a signal on which the first modulated symbol,
and the second modulated symbol the polarity of which is reversed
in accordance with the first modulated symbol with respect to the
first direction in the complex plane are superposed. The reversal
of the polarity of the second modulated symbol brings a plurality
of signal points associated with the same bit group of the second
data series close to each other. Accordingly, the reception device
can appropriately generate the second bit likelihood stream
corresponding to the second modulated symbol stream from the
multiplexed signal that includes the first modulated symbol
stream.
[0545] For example, the second demapper may demap the multiplexed
signal to generate the second bit likelihood stream, based on a
superposition constellation that is a combination of a first
constellation used to map the first bit stream and a second
constellation used to map the second bit stream, and that reflects
the reversal of the polarity.
[0546] Accordingly, the reception device can appropriately generate
the second bit likelihood stream corresponding to the second
modulated symbol stream from the multiplexed signal, based on a
superposition constellation in which a plurality of signal points
associated with the same bit group are brought close to each
other.
[0547] For example, the multiplexed signal received by the receiver
may be a signal on which the first modulated symbol stream and the
second modulated symbol stream are superposed, the first modulated
symbol stream being generated by mapping the first bit stream using
a first constellation in which a plurality of signal points are
dispersed in only the first direction among the first direction and
the second direction, the second modulated symbol stream being
generated by mapping the second bit stream using a second
constellation in which a plurality of signal points are dispersed
in both the first direction and the second direction and being
subjected to the conversion.
[0548] Accordingly, the reception device can receive the
multiplexed signal to which superposition coding is applied in the
first direction. Accordingly, the reception device can receive a
multiplexed signal obtained by superposing, on a single component,
a component that the first modulated symbol in the first modulated
symbol stream includes in the first direction, and a component that
the second modulated symbol in the second modulated symbol stream
includes in the first direction.
[0549] The reception device can receive the multiplexed signal to
which superposition coding is appropriately applied in the first
direction, owing to the second modulated symbol stream adjusted
with respect to the first direction. Accordingly, the reception
device can appropriately generate the second bit likelihood stream
corresponding to the second modulated symbol stream, from the
multiplexed signal.
[0550] For example, the multiplexed signal received by the receiver
may be a signal on which the first modulated symbol stream and the
second modulated symbol stream are superposed, the second modulated
symbol stream being generated by mapping the second bit stream
using the second constellation and being subjected to the
conversion, the second constellation being a constellation in which
noise tolerance in the first direction is higher than noise
tolerance in the second direction.
[0551] Accordingly, this inhibits the influence of noise tolerance
which decreases due to superposition coding, for the first
direction.
[0552] For example, the multiplexed signal received by the receiver
may be a signal on which the first modulated symbol stream and the
second modulated symbol stream are superposed, the second modulated
symbol stream being generated by mapping the second bit stream
using the second constellation and being subjected to the
conversion, the second constellation being a constellation in which
a multilevel number in the first direction is smaller than a
multilevel number in the second direction.
[0553] Accordingly, this inhibits the influence of a multilevel
number which increases due to superposition coding, for the first
direction.
[0554] For example, the multiplexed signal received by the receiver
may be a signal on which (i) a first modulated symbol in the first
modulated symbol stream, (ii) a first component that a second
modulated symbol in the second modulated symbol stream includes in
the first direction, and (iii) a second component that the second
modulated symbol includes in the second direction are superposed,
and a proportion of the first component superposed on the
multiplexed signal may be higher than a proportion of the second
component superposed on the multiplexed signal.
[0555] Accordingly, this makes the first component in the first
direction relatively small, and makes the second component in the
second direction perpendicular to the first direction relatively
large. Accordingly, the reception device can receive a multiplexed
signal in which superposition coding is appropriately applied to
the first component and the influence of superposition coding is
inhibited for the second component.
[0556] For example, the multiplexed signal received by the receiver
may be a signal on which a first modulated symbol in the first
modulated symbol stream and a second modulated symbol in the second
modulated symbol stream are superposed, and in which a polarity of
a component that the second modulated symbol includes in the first
direction is reversed when the first modulated symbol corresponds
to one of two signal points adjacent to each other in the first
constellation, and the polarity is maintained when the first
modulated symbol corresponds to the other of the two signal
points.
[0557] Accordingly, the reception device can appropriately generate
the second bit likelihood stream corresponding to the second
modulated symbol stream from the multiplexed signal in which the
polarity is appropriately controlled.
[0558] For example, the reception device may further include: an
encoder that performs error control coding on the first data series
derived by the first decoder to generate a first bit stream of the
first data series; a mapper that maps the first bit stream to
generate the first modulated symbol stream; a delayer that delays
the multiplexed signal received by the receiver for a predetermined
time length; and a subtractor that subtracts the first modulated
symbol stream from the multiplexed signal delayed by the delayer.
The second demapper may demap the multiplexed signal, with the
first modulated symbol stream being included in the multiplexed
signal as an undetermined signal component, to generate the second
bit likelihood stream, when a signal-to-noise ratio of the
multiplexed signal satisfies a predetermined requirement, and demap
the multiplexed signal from which the first modulated symbol stream
has been subtracted to generate the second bit likelihood stream,
when the signal-to-noise ratio of the multiplexed signal fails to
satisfy the predetermined requirement.
[0559] Accordingly, the reception device can switch, according to
the signal-to-noise ratio, between operation of demapping a
multiplexed signal from which the first modulated symbol stream is
not removed and operation of demapping the multiplexed signal from
which the first modulated symbol stream is removed. Thus, the
reception device can prevent extreme decrease, etc. in the
transmission capacity.
[0560] A receiving method according to an aspect of the present
disclosure is a reception method of receiving a multiplexed signal
into which a plurality of data series have been multiplexed by
superposition coding, and deriving the plurality of data series
from the multiplexed signal, the plurality of data series including
a first data series in a first layer and a second data series in a
second layer, the reception method including: receiving the
multiplexed signal; demapping the multiplexed signal, with a second
modulated symbol stream of the second data series being included in
the multiplexed signal as an undetermined signal component, to
generate a first bit likelihood stream of the first data series;
demapping the multiplexed signal, with a first modulated symbol
stream of the first data series being included in the multiplexed
signal as an undetermined signal component, to generate a second
bit likelihood stream of the second data series; performing error
control decoding on the first bit likelihood stream to derive the
first data series; and performing error control decoding on the
second bit likelihood stream to derive the second data series. In
receiving the multiplexed signal, the multiplexed signal received
is a signal on which the first modulated symbol stream and the
second modulated symbol stream are superposed at a predetermined
amplitude ratio, the first modulated symbol stream being generated
by mapping a first bit stream of the first data series, the second
modulated symbol stream being generated by mapping a second bit
stream of the second data series and being subjected to conversion
in accordance with the first modulated symbol stream in only a
first direction among the first direction and a second direction
perpendicular to each other in a complex plane in which the first
modulated symbol stream and the second modulated symbol stream are
represented.
[0561] Accordingly, the reception device, etc. employing this
reception method can derive the second data series, without waiting
for derivation of the first data series, for instance. Accordingly,
the reception device, etc. employing this reception method can
reduce processing delays. Stated differently, the reception device,
etc. employing this reception method can efficiently perform
processing in a multiplexing scheme that utilizes superposition
coding.
[0562] The reception device, etc. employing this reception method
can receive the first modulated symbol stream, and the second
modulated symbol stream adjusted in accordance with the first
modulated symbol stream with respect to the first direction in the
complex plane. Thus, the reception device, etc. employing this
reception method can appropriately derive the first data series and
the second data series, from the multiplexed signal into which the
first data series and the second data series are appropriately
multiplexed.
[0563] For example, in receiving the multiplexed signal, the
multiplexed signal received may be a signal on which a first
modulated symbol in the first modulated symbol stream and a second
modulated symbol in the second modulated symbol stream are
superposed, and in which a polarity of a component that the second
modulated symbol includes in the first direction is subjected to a
reversal when a component that the first modulated symbol includes
in the first direction satisfies a predetermined condition.
[0564] Thus, the reception device, etc. employing this reception
method can receive, as a multiplexed signal, a signal on which the
first modulated symbol, and the second modulated symbol the
polarity of which is reversed according to the first modulated
symbol with respect to the first direction in the complex plane are
superposed. The reversal of the polarity of the second modulated
symbol brings a plurality of signal points associated with the same
bit group of the second data series close to each other. Thus, the
reception device, etc. employing this reception method can
appropriately generate the second bit likelihood stream
corresponding to the second modulated symbol stream, from the
multiplexed signal that includes the first modulated symbol
stream.
[0565] For example, in generating the second bit likelihood stream,
the multiplexed signal may be demapped to generate the second bit
likelihood stream, based on a superposition constellation that is a
combination of a first constellation used to map the first bit
stream and a second constellation used to map the second bit
stream, and that reflects the reversal of the polarity.
[0566] Thus, the reception device, etc. employing this reception
method can appropriately generate the second bit likelihood stream
corresponding to the second modulated symbol stream from the
multiplexed signal, based on a superposition constellation in which
a plurality of signal points associated with the same bit group are
brought close to each other.
[0567] For example, in receiving the multiplexed signal, the
multiplexed signal received may be a signal on which the first
modulated symbol stream and the second modulated symbol stream are
superposed, the first modulated symbol stream being generated by
mapping the first bit stream using a first constellation in which a
plurality of signal points are dispersed in only the first
direction among the first direction and the second direction, the
second modulated symbol stream being generated by mapping the
second bit stream using a second constellation in which a plurality
of signal points are dispersed in both the first direction and the
second direction and being subjected to the conversion.
[0568] Thus, the reception device, etc. employing this reception
method can receive the multiplexed signal to which superposition
coding is applied in the first direction. Specifically, the
reception device, etc. employing this reception method can receive
a multiplexed signal in which a component that the first modulated
symbol in the first modulated symbol stream includes in the first
direction, and a component that the second modulated symbol in the
second modulated symbol stream includes in the first direction are
superposed on a single component.
[0569] Thus, the reception device, etc. employing this reception
method can receive the multiplexed signal to which superposition
coding is appropriately applied in the first direction owing to the
second modulated symbol stream adjusted with respect to the first
direction. Thus, the reception device, etc. employing this
reception method can appropriately generate the second bit
likelihood stream corresponding to the second modulated symbol
stream from the multiplexed signal.
[0570] For example, in receiving the multiplexed signal, the
multiplexed signal received may be a signal on which the first
modulated symbol stream and the second modulated symbol stream are
superposed, the second modulated symbol stream being generated by
mapping the second bit stream using the second constellation and
being subjected to the conversion, the second constellation being a
constellation in which noise tolerance in the first direction is
higher than noise tolerance in the second direction.
[0571] Accordingly, the influence of noise tolerance which
decreases due to superposition coding is inhibited for the first
direction.
[0572] For example, in receiving the multiplexed signal, the
multiplexed signal received may be a signal on which the first
modulated symbol stream and the second modulated symbol stream are
superposed, the second modulated symbol stream being generated by
mapping the second bit stream using the second constellation and
being subjected to the conversion, the second constellation being a
constellation in which a multilevel number in the first direction
is smaller than a multilevel number in the second direction.
[0573] Accordingly, the influence of a multilevel number which
increases due to superposition coding is inhibited for the first
direction.
[0574] For example, in receiving the multiplexed signal, the
multiplexed signal received may be a signal on which (i) a first
modulated symbol in the first modulated symbol stream, (ii) a first
component that a second modulated symbol in the second modulated
symbol stream includes in the first direction, and (iii) a second
component that the second modulated symbol includes in the second
direction are superposed, and a proportion of the first component
superposed on the multiplexed signal may be higher than a
proportion of the second component superposed on the multiplexed
signal.
[0575] Accordingly, this makes the first component in the first
direction relatively small, and the second component in the second
direction perpendicular to the first direction relatively large.
Thus, the reception device, etc. employing this reception method
can receive the multiplexed signal in which superposition coding is
appropriately applied to the first component, and the influence of
superposition coding is inhibited from being exerted onto the
second component.
[0576] For example, in receiving the multiplexed signal, the
multiplexed signal received may be a signal on which a first
modulated symbol in the first modulated symbol stream and a second
modulated symbol in the second modulated symbol stream are
superposed, and in which a polarity of a component that the second
modulated symbol includes in the first direction is reversed when
the first modulated symbol corresponds to one of two signal points
adjacent to each other in the first constellation, and the polarity
is maintained when the first modulated symbol corresponds to the
other of the two signal points.
[0577] Thus, the reception device, etc. employing this reception
method can appropriately generate the second bit likelihood stream
corresponding to the second modulated symbol stream, from the
multiplexed signal in which the polarity is appropriately
controlled.
[0578] For example, the reception method may further include:
performing error control coding on the first data series that has
been derived to generate a first bit stream of the first data
series; mapping the first bit stream to generate the first
modulated symbol stream; delaying the multiplexed signal that has
been received for a predetermined time length; and subtracting the
first modulated symbol stream from the multiplexed signal that has
been delayed. In generating the second bit likelihood stream, the
multiplexed signal may be demapped, with the first modulated symbol
stream being included in the multiplexed signal as an undetermined
signal component, to generate the second bit likelihood stream,
when a signal-to-noise ratio of the multiplexed signal satisfies a
predetermined requirement, and the multiplexed signal from which
the first modulated symbol stream has been subtracted may be
demapped to generate the second bit likelihood stream, when the
signal-to-noise ratio of the multiplexed signal fails to satisfy
the predetermined requirement.
[0579] Accordingly, the reception device, etc. employing this
reception method can switch, according to the signal-to-noise
ratio, between operation of demapping a multiplexed signal from
which the first modulated symbol stream is not removed and
operation of demapping the multiplexed signal from which the first
modulated symbol stream is removed. Thus, the reception device,
etc. employing this reception method can prevent extreme decrease,
etc. in the transmission capacity, for instance.
[0580] Note that although the above description of the embodiments
illustrates an example in which two data series are multiplexed and
transmitted on the two layers to simplify the description, it is
clear that the present disclosure is readily extendable to
multiplexing and transmitting three or more data series, following
the embodiments.
[0581] Also, FIG. 1, FIG. 13 to FIG. 15, and FIG. 24 to FIG. 26
illustrate an example in which a radio-frequency signal is sent
from an external antenna connected to the transmission device that
does not include an antenna, but the transmission device may
include an antenna such that a radio-frequency signal is sent from
such an antenna of the transmission device.
[0582] Also, FIG. 2, FIG. 7, FIG. 16 to FIG. 19, and FIG. 27 to
FIG. 30 illustrate an example in which a radio-frequency signal is
sent from an external antenna connected to the reception device
that does not include an antenna, but the reception device may
include an antenna such that a radio-frequency signal is sent from
such an antenna of the reception device.
[0583] Also, the antennas used to send/receive a radio-frequency
signal may be an antenna unit that includes a plurality of
antennas.
[0584] Although not illustrated in FIG. 1, FIG. 13 to FIG. 15, and
FIG. 24 to FIG. 26, the transmission device may include a frame
configuration unit that arranges a superposed signal generated by
the adder in accordance with a predetermined frame configuration to
generate a frame, and outputs such a frame into the RF unit.
[0585] Here, the configuration of a frame generated by the frame
configuration unit may be uniform, or may be changed in accordance
with a control signal sent from a controller not illustrated. The
frame configuration unit arranges, in a frame, a superposed
modulated symbol stream in which the first data series and the
second data series are multiplexed, in accordance with a
predetermined rule.
[0586] The frame generated by the frame configuration unit may
include a pilot symbol, a control information symbol, a preamble,
etc. in addition to a data symbol. Note that a pilot symbol, a
control information symbol, and a preamble can each be referred to
by another name.
[0587] For example, a pilot symbol may be a symbol that is
generated by mapping a bit stream known to the reception device on
the basis of PSK modulation such as BPSK and QPSK. A pilot symbol
may also be a symbol that includes an amplitude and in-phase (or
complex value) known to the reception device. A pilot symbol may
also be a symbol, according to which the reception device can
estimate the amplitude and in-phase (or complex value) sent by the
transmission device.
[0588] Then, the reception device uses the pilot symbol to perform
frequency synchronization, time synchronization, channel
estimation, etc. on the received signal. Channel estimation is also
referred to as the estimation of channel state information
(CSI).
[0589] A control information symbol is a symbol used to transmit
information that should be notified to the reception device as
information required to demodulate a received signal and obtain a
desired data series.
[0590] For example, the transmission device sends a control
information symbol corresponding to control information. The
control information may indicate the mapping (modulation) scheme
and error control coding scheme used for each data series, the code
rate and code length of the error control coding scheme, and the
positions where the modulated symbols of each data series are
arranged in a frame, etc. The reception device demodulates the
control information symbol to obtain the control information. The
reception device then demodulates a data symbol on the basis of the
obtained control information to obtain the data series.
[0591] The control information may also include information used to
control the operations of an application, such as settings
information for an upper layer.
[0592] A preamble is a signal added at the leading end of a frame.
For example, the reception device may receive a signal that
includes a preamble to perform processes such as frame detection
and frame synchronization on the basis of the preamble. A preamble
may also include a pilot symbol and a control information symbol. A
frame may also include not only a preamble but also a postamble,
which is a signal added at the rear end of the frame.
[0593] The encoders use low density parity check (LDPC) coding,
turbo coding, etc., for example, as the error control coding
scheme. The encoders may also use another coding scheme.
[0594] The transmission devices illustrated in FIG. 1, FIG. 13 to
FIG. 15, and FIG. 24 to FIG. 26 include their respective
interleavers, but may not include interleavers as described above.
In such a case, the transmission device may input a bit stream
generated by each encoder directly into each mapper or may perform
a process different from interleaving on the bit stream before
inputting it into each mapper. When the transmission device does
not include any interleavers, the reception devices illustrated in
FIG. 2, FIG. 7, FIG. 16 to FIG. 19, and FIG. 27 to FIG. 30 may not
include any deinterleavers.
[0595] The deinterleavers of the reception devices illustrated in
FIG. 2, FIG. 7, FIG. 16 to FIG. 19, and FIG. 27 to FIG. 30 perform
permutation on the basis of a permutation rule that is a reverse
rule of the permutation rule used by the transmission side, but may
perform an operation different from such permutation. For example,
each deinterleaver may input into the corresponding decoder a
plurality of bit likelihoods of a bit likelihood stream generated
by the corresponding demapper in the bit order required for
decoding performed by the decoder.
[0596] In the above description, although superposition coding and
the variation of superposition coding are applied to wireless
transmission, but the present disclosure is not limited to the
application to wireless transmission, and thus may be applied to
wired transmission, optical transmission, etc. and also to storage
into a recording medium. A frequency band used for transmission is
not limited to a radio-frequency band, and thus may be a
baseband.
[0597] "A plurality of" used in the present disclosure is
synonymous with "two or more". Ordinal numbers such as first,
second, and third may be removed from the expressions, replaced by
other wording, or newly added as appropriate.
[0598] Note that the devices, methods, etc. according to the
present disclosure are not limited to the respective embodiments,
and thus allow for various modifications for implementation. For
example, in the embodiments, the technology of the present
disclosure is implemented as a communication device (transmission
device or reception device), but the technology of the present
disclosure is not limited to this, and thus may be implemented as
software used to execute a communication method (transmission
method or reception method) executed by such a communication
device.
[0599] Also, two or more structural components of the transmission
device or the reception device may be integrated as a single
structural component, and a single structural component may be
divided into two or more structural components. Also, the
transmission device and the reception device may form a single
transmission/reception device. In such a case, a plurality of
structural components of the same kind may be integrated into a
single structural component. For example, a transmission antenna
and a reception antenna may be formed by a single antenna.
[0600] Also, for example, a process performed by a specified
structural component may be performed by another structural
component. The order of performing processes may be changed, and a
plurality of processes may be performed in parallel.
[0601] Note that a program for executing the above-described
communication method may be previously stored in a read only memory
(ROM) to be executed by a central processing unit (CPU).
[0602] Moreover, the program for executing the above communication
method may be stored in a computer-readable recording medium. Such
a program stored in the recording medium may be recorded in a
random access memory (RAM) in a computer so that the computer may
execute the communication method according to the program.
[0603] Note that each of the structural components according to the
embodiments, etc. may be implemented as a large-scale integration
(LSI), which is typically an integrated circuit. The structural
components may take the form of individual chips, or one or more or
all of the structural components according to the embodiments may
be encapsulated into a single chip. Although LSI is illustrated
here as an example, such chips may be referred to as integrated
circuits (ICs), system LSIs, super LSIs, or ultra LSIs, depending
on their degree of integration.
[0604] The ICs are not limited to LSIs. Each of the structural
components thus may be implemented as a dedicated circuit or a
general-purpose processor. Afield programmable gate array (FPGA)
that allows for programming after the manufacture of an LSI, or a
reconfigurable processor that allows for reconfiguration of the
connection and the settings of circuit cells inside an LSI may be
employed.
[0605] Furthermore, when the progress in a semiconductor technology
or another derivative technology results in a new IC technology
that replaces LSI, such new technology may of course be employed to
integrate the devices or some of their structural components
according to the embodiments. For example, adaptation to
biotechnology is possible.
[0606] Furthermore, when the progress in a semiconductor technology
or another derivative technology results in a new IC technology
that replaces LSI, such new technology may of course be employed to
integrate the devices or some of their structural components
according to the embodiments. For example, adaptation to
biotechnology is possible.
[0607] In this disclosure, the phrase of "at least one of A or B"
should be interpreted that the phrase includes only A, only B, and
both A and B.
[0608] Although only some exemplary embodiments of the present
disclosure have been described in detail above, those skilled in
the art will readily appreciate that many modifications are
possible in the exemplary embodiments without materially departing
from the novel teachings and advantages of the present disclosure.
Accordingly, all such modifications are intended to be included
within the scope of the present disclosure.
INDUSTRIAL APPLICABILITY
[0609] The present disclosure is applicable to a wireless
communication system and a broadcasting system, etc. The present
disclosure is widely applicable to a system for multiplexing a
plurality of data series by superposition coding.
[0610] The present disclosure is also applicable to a wired
communication system, etc. such as a power line communication (PLC)
system, an optical communication system, and a digital subscriber
line (DSL) system. The present disclosure is further applicable to
a storage system, etc. for recording data into a recording medium
such as an optical disk and a magnetic disk.
* * * * *